Oil leak due to crankshaft end play

Crankshaft end play is controlled by the thrust bearing which is part of one of the crankshaft bearings. If there are no other problems, it is acceptable to replace that bearing, but you will usually have to buy the complete set. Chemical additives keep rubber seals pliable so they will bend to seal to items that are moving away from their lip a little. That could apply to a worn front crankshaft bearing that is allowing the snout of the crank to move up and down a little. Additives do not work when the sealing surface moves away from the lip seal. That is what happens when the crankshaft walks back and forth. The movement has to be rather significant to cause a leak at the front main seal. Typically 1/8" of end play wont be enough to pull the snout back far enough that the lip of the seal runs off the machined surface. Excessive end play is more likely to push the front seal out of its housing, and that is when the leakage occurs. If your seal is still in place, I would suspect it just needs to be replaced.