I flush the brake fluid every 1 year on all the cars. Brake fluid is cheap insurance on replacing calipers. Remember that DOT 3 will absorb LESS moisture than DOT 4. While the boiling point on DOT 4 is higher, unless you are an autocross racer, the DOT 4 is NOT needed.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

I buy the high(er) end stuff that comes in a metal can and has a bunch of German writing on it at Halsey Import here in Portland. They specialize in german automotive products so I figure it must be good stuff

I usually buy it in the 5 liter metal can from fastlane with the big "SL" on it... er hast Deutsch on it as well With 5 liters I can just fill the power bleeder with a ton, and bleed away on both cars as much as I want.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The Great DOT Brake Fluid Controversy

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Of my 7 cars, I only refresh the brake fluid in the 2 w/ ABS. That is because I use silicone fluid in the other 5, including my two 300D's. The fluid stays perfectly clear (w/ blue tinge) and no more rust. There is an amazing amount of mis-information about silicone fluid. Yes, I read WHunter's story of a friend who switched to silicone, and some time later crashed in a ditch when a brake hose failed. The failure theory was that silicone "allows" water drops in the fluid, which flashed to steam, raising the pressure in the system, which burst the hose. Interesting, but too many technical errors to even address. Did anyone suspect the hose might have just been old?

I have an MS in Mechanical Engineering, so figure I can decide for myself. Silicone is more benign than glycol. Indeed, some British sports cars in the 1950's required silicone since glycol attacked the seals. Glycol absorbs moisture from the air, which is why it needs regular flushing, especially if you live on the Gulf Coast. Look up "diffusion" for more info. There is no mechanism by which silicone would attract water. True, if water drops into it, it will stay as unmixed drops, but that might be good. Don't let water drip in your master cylinder (with any fluid). No problem if silicone touches left-over glycol. They don't mix. The only issue is that the bad glycol will be spots that can rust.

DOT 5 does not equate to silicone. It is a standard that only silicone could meet until recently. There are now glycol fluids that meet the DOT 5 standard, so the DOT made them label them 5.1 to distinguish, but I'm sure it still confuses people. The glycol will still cause rust.

Silicone is not qualified for use in ABS systems. I don't know if because they know it won't work as well or they just never tested it. It is slightly more compressible than new glycol. However, as glycol absorbs water vapor, its properties degrade, so the real question is would silicone be worse than typical old glycol? I don't have time to experiment, so I use glycol in my ABS cars. Despite what people claim (who never used it?), silicone does not cause a noticeably spongy pedal. My pedals are all hard. It takes very little effort to pour it in without getting air bubbles, you just pour it down the side of a funnel, don't splash it in like a fool. If you drop the bottle, let it sit a few hours before you pour it, so any air bubbles settle out. If still concerned, let it sit in the reservoir a few hours before you start bleeding (I have never seen a bubble). If working at home, I am sure there are other things to occupy you (yard, fix house). When I drain my oil, I pull the plug Friday after work and let it drain until maybe Sunday afternoon. A shop couldn't do that.

Finally, don't pay extra for "synthetic brake fluid". That is clever marketing hype. All brakes fluids, both glycol and silicone are "synthetic", i.e. man-made, not occuring in nature (mineral).