Is there an additive that will stop a rear main seal leak?
Unfortunately not. Seals usually leak because of excess pressure, the shaft they are sealing starts to move or more likely in this case, because they have gotten hard. The most common cause of seals getting hard is not frequent enough oil change intervals. Additives claim to work by swelling seals. This normally has the effect of breaking down the rubber and making not only this, but all seals in the engine far worse. A proper repair will not only be effective, it will be far less expensive in the long run. A more detail article on change interval is in our Detailed Auto Topics section under The Sad Truth.
