I've seen some quotes from a reputable Polaris engine builder named Indy Dan who says to never use synthetic oil because it doesn't stick to the internals of the engine (bearings, seals, etc.).
When I tore down my doo 800 & all engine parts were coated with Blue Marbel but BM is a mineral oil not synthetic. The feel of the oil flim was impressive ....ahhh my bygone 2s days. lol