My mechanic said the rear main seal on my 1997 Honda Accord is causing an oil leak, and he cannot fix that.

I found out there are some oil leak stopping products (such as this, this, this, this) that are some sort of fluid that you can pour into your engine to stop a rear main seal leak or a general oil leak. There are many positive reviews from people who said the products stopped their oil leak. I also found some comments on automotive forums from people who basically said they wouldn't touch these products with a 10-foot pole.

Could there be any harm in trying one of these oil leak stopping products?

  • I would not use it on my engine, but you can tell us how it goes .
    – Solar Mike
    Oct 7, 2021 at 19:24
  • I also would not use these products. They advertise that they contain chemicals that cause rubber to swell but they affect all rubber pieces in the engine. Some of those may be adversely affected by swelling. I think your best bet would be just to live with it and keep an eye on your oil level. If the leak becomes too troublesome then a seal repair may be in order but you may want to consider the cost for a vehicle this old.
    – jwh20
    Oct 7, 2021 at 20:12
  • 1
    If it is an old car that you just want to keep going for a while without spending much money on it, then it is probably worth a try.
    – HandyHowie
    Oct 7, 2021 at 20:37
  • How much does it leak ? I had a GMC that made a mess in the garage but it only lost less than a quart per month. So I put cardboard on the garage floor and changed it once in a while. I would never try a sealer. Oct 8, 2021 at 0:49
  • I could have sworn this is a duplicate but I can't find the original.
    – GdD
    Oct 8, 2021 at 7:44

1 Answer 1


Before you use those products, try one quart of Marvel Mystery Oil in the crankcase with an oil change. Run the car for 300 miles, change oil & filter and repeat the MMO treatment. If you notice any change, even if the leak becomes worse, repeat the same dosage with another oil change after 1,500 miles. If the leak improves gradually, perform a third oil change & MMO treatment for an additional 1,500 miles. There is a good chance the leak will disappear after totaling 3,300 miles.

I fixed several leaks throughout my engine in this manner, including the rear main. The reason turned out to be micro-sediments in the engine had broken free and become lodged in the seals. The MMO gradually dissolves the sediments and thereby restores proper seal function. In the process of doing so, the MMO forces some sediments past the seal, which is why the leak may get temporarily worse. Do not become alarmed, since the MMO can in no way alter or damage the seals or any engine parts. In fact, you can use one quart MMO indefinitely in the crankcase for the life of the engine for superior wear protection and cleanliness.

I have used the ATP AT-205 Re-Seal with success. The key was to use only 2 oz. instead of the whole bottle. Give it time to work, approximately one month & 1k miles of driving, before adding two more ounces on a fresh oil change.

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