We only fill rotation holes and on end of seal as recommended have had no issues. We have used 1 and 2 piece seals the one thing I can say is 2 piece so much easier to install. My engine has had a 2 piece in it since 2012 and has been run hard with no leaks. Crankcase pressure is going to make your engine leak faster than anything else except for a complete gasket failure. The last rear seal we saw leaking was a two piece but after a little investigation we found out the owner had removed the pan and rear cap in car and slipped it in It failed miserably.
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