I have a 240 sedan that is leaking what appears to be oil down by the Y of the exhaust pipe. It is not coming from the oil pan. I've been told it is possibly the rear main seal. Would this be true? How hard is it to fix and how is it fixed?

I would look higher on the engine to see where it is coming from.
A leak at the rear Cam plug will cause oil to run down the back of the engine and possibly on the pipe.
Slide you hand down the Back of the Head from the rounded part of the Valve Cover until you feel the round disc ( About 1" in diameter). Is that area all soaked in oil?

Also look at the front of the engine, is there signs of Oil on the Waterpump. Oil from the Cam Seal will run down the engine and the wind force from driving will spray it on the exhaust.
I wouldn't rush the Rear Main seal conclusion.
--
'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html

Flame trap jiggle test: With the engine idling, unscrew the oil filler cap on the valve cover and let it sit there. If your flame trap IS clogged causing pressure to force oil out, the cap will jiggle. The ipdusa.com website has a decent diagram of the flametrap, or if you have a Bentley manual... If the flame trap is not clogged, the vacuum of the intake manifold will hold the cap down such that it won't jiggle. Even if the flame trap is working properly, you can start with simple things like the rubber plug mentioned and a new valve cover gasket at the same time. From time to time I give the 10mm valve cover cap nuts a very slight turn, about once a year.
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1988 245A. Past: 1979 245A; 1987 244 M47; 1971 164E

OK, I unscrewed the oil cap and it jiggles. When I first noticed the oil drip it was coming out at a pretty fair rate. Today it appears to be a little slower.
I had put a quart of oil in the other day when I first posted my question and hadn't touched the car until today. Both the transmission and oil levels appear to be good. I am far from a mechanic so what would be my next step?
Thanks, Tom

If your 1992 is like my 1988, there is a flame trap in the Positive crankcase venitlation (PCV) system. If it is clogged for a long time, there can be a pressure build-up in the crankcase.

The rear main seal, and other seals exposed to crankcase pressure (cam shaft, I-shaft, front main), are subject to more pressure than they are designed to hold. Usually it is the rear main seal that develops a leak.

Of all those seals, the rear main seal is the biggest repair project, since replacement requires removal of the transmission.

When my 1984 240 developed such a leak, I chose to thoroughly clean the PCV system including both the hoses and a new flame trap. The result was a 90% drop in the amount of oil leaked out. Still leaked, but enough to live with.

My 1988 240 is on Mobil-1 oil, so the flame trap never clogs. I vaguely recall a notice that it is OK to discard the flame trap altogether. If that is not correct, Art B. will correct me.

By the way, the rear main seal itself might cost $25. The labor and other parts needed to do the replacement cna run $400 +/- .

Good Luck,

Bob

:>)

It is hard to determine the source of a leak just by where it drips off of the car. First determine that it is indeed oil and not transmission fluid. The transmission cooler lines run right by there and rub through at the bracket. The best approach to finding oil leaks is a thorough cleaning and frequent re-inspection. Often with our old cars, several oil leaks combine, and it helps to know which are the ones needing the most urgent attention.
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Art Benstein near Baltimore

Drive carefully. It's not only cars that can be recalled by their maker.

Agree with Art,

Also slide you hand (after the engine cools off) on the back side of the engine just below the valve cover and see if the rear Cam Seal is trying to pop out. Oil can run down the transmission housing and hit the exhaust if you get a leak there. That will not be a little leak if the thing pops all the way out by the way.

If that is the problem, Clean your flametrap and make sure the block has good negative pressure.

Regards,

Paul

My favorite cleaner for doing this kind of exploration is brake cleaner. It's fairly cheap, and doesn't leave any oily residue, so you can start fresh. A mechanic's angled mirror is a handy tool for seeing if your rear cam cover seal is leaking or blown out of position, too.