I think I've greatly alleviated my Rear Main Seal leak. First a little history.

Bought the car eight months ago. Didn't know what oil they had put at the dealership, but it was new, so I drove a couple of thousand miles with it.
I noticed the car was leaking some oil - just a small amount, so that I can see it on the ground and annoy me.

I then switched to Mobil 1 10W40 and the leak became bigger. It got to the point where I would lose 1qt per 400 miles!!! Put a bottle of Bar's Rear Main Seal fix...it did absolutely nothing.

I then followed the advice of a friend of mine (Jag owner, so he is familiar with leaking fluids) and bought a bottle of Valvoline MaxLife 10W40 Synthetic Blend. I only put half a bottle of it and since then I've driven 300 miles - no oil loss!!! There are still a few drops under the car, but it's not as monumental as before.
So for anyone who has a RMS problem and wants to postpone fixing it for a while, I suggest you try the Valvoline MaxLife! I'm really impressed!

(the other thing I noticed after putting the Valvoline in is that I can check my oil level accurately after just 20 minutes. With the Mobil 1 I had to wait a good 3-4 hours until the oil would go all the way down to the pan so I can accurately measure it)

 

I had the same issue with my car. I had a front crank seal that was leaking about a quart of oil every 500 miles. I tried the Valvoline MaxLife, but it did not seem to make a big difference. I ended up switching to Mobil 1 High Mileage and it has slowed down significantly. It may have stopped all together but I don't want to jinx myself.

So anyway, try the Valvoline first and if that does not seem to stop the leak, then try the Mobil 1 High Mileage.

 

I tried Mobil 1 high mileage on mine and it did absolutely nothing to slow down the leak. I used it for 14,000 miles.

 

All of the "high mileage" oils work on one of 2 principles... they're either a bit thicker and stickier, or they contain a chemical that softens rubber seals. If a seal is leaking because it's hardened, the softening type will work... for a little while. The softened rubber wears a LOT faster. The other type can reduce... temporarily... leaks from cracked or otherwise physically damaged seals. All of these high mileage oils are merely regular oil with some of the old- fashioned "mechanic in a can" wonder fluids like Motor Honey, Bar's leaks, or Restore, already added. And they work about as well... they'll slow or stop a leak for a month or three... that's it. There's no magical cure for bad seals.

 

Well, according to my friend, the Valvoline MaxLife is the ONLY third-party tested and proved to meet its claims oil on the market.

I'll report again, after I drive some more this weekend.

 

Carrots is 100% correct! If a seal is damaged....................there is no cure!! The seal has to be replaced! I remember putting oatmeal in the radiator years ago. Worked fine until you built up pressure by driving at a higher rate of speed. Nothing lasts forever and especially in an auto as old as the 850's are.

r.

 

Well, yes...it's not going to fix the seal, but at least it will postpone the change for a while.

 

UPDATE:

In January I changed the oil to the above mentioned Valvoline MaxLife 10w40. Two months, and 1,000 miles later - no oil loss.

I can still see a few drops of oil on the ground, but nothing scary. And the fact that I haven't had to add oil is impressive. I like this oil