[ammonman]

The seal leak issue is very dependent on the quality of conventional lubricant used over the life of the unit, change interval, and any thermal abuse with high moisture contamination in the lubricant. Excessive heat, moisture, and any wear metals in the lubricant combine to form acids and/or bases along with varnishes. Top quality modern synthetics remain stable at much higher temps and with greater moisture/wear metal loading than conventional oils. If you have an engine with a known history of quality conventional lubricant, on time oil changes, and minimal "short cycling" where the oil doesn't come fully to temp before the engine is shut off to drive out moisture then switching to synthetic generally will not result in new leaks. That said, the change make cause existing leaks to get worse. YMMV