hi, 1991 240 with only 120,000 and rear seal is leaking badly.

Do any of those oil addatives that supposedly soften or swell
seals really do any good? I thought maybe something with
the word "miracle" in it's name. :-)

thanks, Jon

I had a hell of a rear main seal leak on my '83 GL within weeks after I bought it, around '86. The flame trap was plugged solid, and the excess crankcase pressure had forced the rear seal outta its housing.

Had to pull the tranny back and install a new seal.

And do a roto-rooter job on the crankcase ventilation system.

A few years back, I had the big plug in the rear of the head pop out from my '86. MASSIVE oil leak. Same cause. After installing a new plug, I made and installed a retaining strap across the plug (see below).

I'd avoid any miracle crap in the engine. If it was any good, it would truly be a miracle. Since miracles don't exist, the crap is not truly good.

Heheh.. you mean miracles don't exist? RATS! I know, I'm having a weak moment, I've never used those fancy additives in my cars. Recently though I heard those Car Guys, CLick and CLack, saying anything with the word "miracle" in it works great, the more the better! LOL Oh well. Oh, and I checked that plug in the head with a little dentists mirror, it's fine. And cleaned the flame trap too.

How difficult what that rear seal install? What's my mechanic in for?

Thanks for all your help. :-) Jon

"Recently though I heard those Car Guys, CLick and CLack, saying anything with the word "miracle" in it works great..."

If Click 'n Clack said that, then they were laughing the whole time. Those guys are amazing -- one has a Ph.D. (from BU, I think), and the other has an engineering degree from MIT. Or approximately that. They got more degrees than a thermometer.

"How difficult what that rear seal install?"

Pulling an automatic transmission properly is not really a light-weight job, literally. The AW71 weighs in at about 165-170 pounds and is a bitch to control when you're under it with a jack. It's a job best done on a lift and using a proper tranny jack. And it's best to have some experience with the job. Plus, you need a 4' extension to remove 'n install the top bellhousing bolts. Of course, you can do it in a garage lying on your back, but it's risky and tedious.

"What's my mechanic in for?"

He'll be solidly in your wallet. You'll probably pay a good portions of his kid's first year at college. If you do, then tell him you get to select the kid's courses.
--
Don Foster (near Cape Cod, MA)

"Seal savers" work by adding a chemical such as alcohol to the oil. This is absorbed by some seal materials and causes them to swell, temporarily sealing the leak. The long-term cost is more seal wear on all the seals, not just the leaker. Your front seals are close to the point at which they need to be replaced anyway.

The advice rendered earlier is very good: first check the crankcase breather system to make sure it is not causing a problem. Then, if you really have to and cannot afford to fix the seal, add the oil additive.

Before adding anything, make sure that the engine ventilation system (flame shield) is not clogged. If it is, the engine will build pressure in the oil sump and force oil out of a seal somewhere. With it running, loosen the oil filler cap and see if it pushes it up and blows air out, if it does clean the system. If this is causing the problem, the rear seal may stop leaking.

oops, I forgot to mention that I'd just cleaned the flametrap/crankcase vent and there's good vacuum at the oil filler cap at any RPM. I'm pretty sure it's the main seal.

I have the same problem on my 940 (Thanks to synthetic ...Mobil 1) and have been feeding it oil to put off the inevitable.

The only price I have gotten so far is $270 but that sounds high to me??? Anyone priced rear main seal lately?
Chris