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Old 07-29-2003, 12:07 PM
ebennz's Avatar
Join Date: Nov 2000
Location: Hurricane, West Virginia
Posts: 878
rear main seal-revisited

i've searched the archives, but still have a few questions...

if the rear main is leaking [a little bit] can the car still be used?

is it UNWISE to drive and use in this condition?

will the leaking eventually cause a problem with torque converter or transmission?

would having the head redone make it easier to replace this rear main?

i may just bite the bullet and have head redone, alternator replaced, and rear main seal done at once since these are [probably] the next to die on a m103 with 146k on it?



*92 400e 124.034, SOLD

*92 300e 124.030, SOLD
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Old 07-29-2003, 12:18 PM
dtf dtf is offline
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Join Date: Jul 2003
Location: South East CT
Posts: 824
More technical people will chime in but I think you can drive it while it is leaking - just keep an eye on the oil level. The rear main seal keeps the engine oil in the lower part of the engine and I don't think it should affect the transmission. Working on the head has nothing to do with the rear main seal (I think). Mine is currenlty leaking a little but it has not increased in almost 30,000 miles.
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (203,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles)
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (124,034 miles)
2014 E350 4Matic Wagon 48,000 miles
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Old 07-29-2003, 12:29 PM
Posts: n/a
Since it is an automatic, there is not a down side to a SMALL leak except for the mess. With a manual transmission you risk oil soaking the clutch disk.

On your car, unlike many MB's, the pan can be removed without removing the engine. This does make it feasible to replace the seal without removing the engine. After saying that, I now wonder if the M103/104 engines have a one piece rear main seal that would require removal of the transmission.

Maybe someone can chime in regarding whether these engines have a one piece or two piece seal.

Good luck,
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Old 07-29-2003, 01:16 PM
engatwork's Avatar
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 11,773
On the 104 engine you do have to remove the tranny to replace the rear main seal. I suspect the same is true on the 103 engine too.
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Old 07-29-2003, 02:21 PM
Registered User
Join Date: Nov 2001
Location: North Central Kentucky
Posts: 1,065
Just pulled up the cd for my 201 body. On the 201 with the 103 engine, the rear main is ONE piece. Oh well! That said, if it isn't leaking too much, you can live with it. Just keep the oil level up and maybe figure out how fast it is leaking so you can watch for changes.
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Old 07-29-2003, 02:29 PM
blackmercedes's Avatar
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Join Date: Dec 2000
Location: St. Albert, Alberta, Canada
Posts: 3,492
I agree that this is not an urgent repair unless the leak becomes quite severe. As Larry pointed out, if you had a manny-tranny, thent he seal should be done right away to keep from oil soaking the clutch, but since you have an automatic, that is not an issue.

One of my 190E's had the rear main seal start weeping at about 180K and didn't get changed until the tranny came out for a rebuild at 400K.
John Shellenberg
1998 C230 "Black Betty" 240K
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Old 07-29-2003, 02:31 PM
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Join Date: Aug 2001
Location: At Sea
Posts: 1,729
look up the TSB for the revised oil capacities. overfilling can cause main seal failures and the info on some of the user manuals was a bit on the high side. mine was weeping a bit when i got it. i followed the revised guideline and it has slowed to a negligible drop or two over the past two years...
1993 300e-2.8
- gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"
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Old 07-29-2003, 06:56 PM
blackmercedes's Avatar
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Join Date: Dec 2000
Location: St. Albert, Alberta, Canada
Posts: 3,492
Originally posted by jsmith
overfilling can cause main seal failures and the info on some of the user manuals was a bit on the high side.
Yes, it can ruin both front and rear main seals. If the crankcase is overfilled, the oil is hit by the crank journals. It "bubbles" (the proper term is cavitation) and the oil/air "mixture" is highly abrasive. Anyone who boats knows the prop damage that can result if it cavitates.

Anyway, the cavitation will destroy the seals in a surprisingly short time. My dealer overfilled the C230 and it wrecked both main seals in no time. That was the last time they were allowed to change my oil, and since doing it myself, no problems.
John Shellenberg
1998 C230 "Black Betty" 240K
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Old 07-30-2003, 08:35 AM
Posts: n/a
So, it sounds like this engine has a one piece seal. Actually that makes it easier to replace the seal than if it were a two piece in a 123 which requires pulling the engine.

In most cases it is quicker to pull the transmission than it is to pull the engine. Since the 124, however, could be changed if it were two piece since the pan will come off without pulling the engine, then it may be a wash.

Good luck,
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