Rear main seals leak or weep for only a couple of reasons. Usually they get
dirty. And by that I mean a layer or more of oxidized oil will form on the
crank journal, that is not a perfect match to the polymer seal lip. Or the
seal material has some crust on it over time and can change its shape. Also
the PCV valve could be under performing, trapping high amounts of positive
pressure in the motor cavity. This can force oil out of the weakest seal,
which is typically the rear main. Or lastly the seal is either worn or
cracked, or the crank journal is out of balance. Auto-Rx can help with the
cleaning end. Only a replacement will fix a worn or torn seal.
We do suggest running Auto-Rx with a conventional oil for the clean and
rinse phases of the application. After the rinse phase, feel free to switch
back to your full synthetic. The reason why suggest conventional mineral oil
is as follows: Mineral oil tends to shrink down the seal material and
stiffen it to some degree. This helps it find it's old memory to create a good
lip seal with the crank journal. Whereas synthetic oils tend to keep the
seal material more soft and supple and in most cases won't reseal.
So I highly recommend that you check or replace the PCV valve, with an oem
part. Then run a single bottle of Auto-Rx in a fresh fill of conventional
oil, for 3000 miles. Then follow it up with a rinse of 3000 miles on
conventional oil, with no new Auto-Rx added. This is your best shot. Once
the leak has stopped feel free to go back to whatever oil you choose.
Rich
