I’m at around 205,000 miles, still on the original. Noticed some weeping around the brake booster over the weekend. Could be the rubber grommets at the reservoir, could be the master cylinder finally losing its internal seal.

Curious how long you guys have been running yours?

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1981 240D 4sp manual. Ivory White.

In my previous SDL it lasted over 300,000 before it went to the floor when I bled it improperly.

Damn near forever

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

No set in stone span. They go when they go.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

How well the fluid has been maintained over the life of the car plays a major role in how long the master cylinder (and the calipers) lives. Brake fluid is hygroscopic and accelerates wear and corrosion of the metal parts in the brake system as it accumulates water from the atmosphere. A car that has the fluid changed and flushed every 2-3 years will enjoy significantly longer lifespan of brake parts and a much better feeling pedal than a car that has the fluid changed only when something breaks.

As mentioned above, there's no set in stone value for lifespan, but you can do your part to prolong the life of the entire brake system by changing the fluid every couple of years.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Yes, MB specified maintenance interval is 2 years on brake fluid. I think it has been that way going back to 1970s.

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-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991

As mentioned, the periodic flushing & bleeding is wise .

Usually it's the first serious cold snap that causes master cylinder failures, I'd always stock up in September, November they'd begin rolling in .

As you're seeing seepage now, I'd check the pads then buy a new one and a big bottle of fresh brake fluid .

A pressure bleeder is $50 and well worth the $ in time saved and better flushing done, maybe cheaper slightly used ? .

I never put fluid in mine, I only use it as a pressure device, it should last longer that way .

Anytime I see black brake fluid I want to flush and bleed the system .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I appreciate the maintenance tips -but mainly concerned with long they’ve lasted on your individual vehicles.

I flush my system every two years with a power bleeder. I currently have no issues with my brakes, but as these cylinders seem to fail catastrophically when they do fail, I’m curious how long those of you -who do perform regular maintenance- are getting out of them.

edit: this tutorial on changing the reservoir seals is what prompted my curiosity, https://www.ifixit.com/Guide/Mercedes+W123+Brake+Reservoir+Rubber+Seals+Replacement/27809
In the archives, I couldn't find many references to these seals. It seems that most simply change the entire apparatus which seems like a waste. Hence my question...

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1981 240D 4sp manual. Ivory White.

Since I just recently had a MC fail (Dec. 2019)... Purchased the car in 2005, no idea on the MC age at the time. Since then the fluid has been changed whenever I've had 'other' brake issues, not exactly as the suggested interval (I know - I know) but... anyway, x2 front calipers due to sticky calipers and once again for rear line rust through (car was a New England refugee)
15yrs is not a bad run considering sub par maintenance.
Failure mode is pretty dramatic, one morning the pedal just drops to the floor, though braking can be achieved by pumping until the fluid is gone.
There are some warning signs though such as low fluid with no visible leaks ANYWHERE.
When I pulled the MC the vacuum chamber was filled with the leaked fluid.

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1985 300D
The rest:
1957 MGA (comatose)
1965 Falcon (sleeping)
1966 E-100 (rust test in progress)
1976 Ford 3400 D Tractor (workhorse)
1978 Mercury Zephyer (5L playtoy)
1995 Isuzu NPR D (fetcher)
1998 Subaru Legacy (Spare)
2000 Toyota Sienna (School bus)
2008 Toyota Prius (Commuter)

Mine failed at around 185K. I don't think the number of miles is likely as important as the age, climate conditions, vehicle use and regularity of brake fluid changes.

Dkr.

My 300CD is 35 years old and I replaced the original master cylinder because the grommets were leaking and I figured the original had done enough! Did not want to push it much longer when I could still find a new one for the next 35 years.

Since you're talking about weeps from between the master and booster I'd say get a new one PDQ ~ when the brakes failed in my graymarket '84 it was raining and I was headed down a ramp towards a locked truck proof security gate .

Scared the crap out of me .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Putting new seals in used to be SOP and we had 2 - 3 brake hones of various sizes in the tool box. (I found some the other day and put new o-rings on them to keep the arms from getting lost.) Now, parts are so inexpensive that it's tempting to just install another. If yours is weeping anywhere, it needs to be dealt with - now.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Thanks all -As soon as I noticed the leak, I did order a new ATE cylinder.
I just really dislike firing the parts canon unnecessarily, so wanted to make sure this was not one of those instances.

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1981 240D 4sp manual. Ivory White.

What a GREAT comment ! .

You're in L.A. so there was the possibility of buying a good used master cylinder, I know many are afraid to but if you know what you're about it's do - able, I've done it in a pinch and never had a problem / failure .

Indeed, $pending the Lolly when there's Pizza or liver & onions to be had, is no fun .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

There were other options, to be sure. But in this case (brakes!), pennywise pound-foolish etc, $80 wasn’t too hard to swallow.

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1981 240D 4sp manual. Ivory White.