I'd read quite a few opinions about synthetics in general causing seal weepage- didnt harm the seals, supposedly the oils just prone to seep anywhere- part of its better lubricating qualities is smaller molecules or some bs that can encourage seal seeping- especially if put in a older motor that was run in with conventional lube, and already has a polished seal surface...general opinions were if using synthetics to do so on newer engines, as putting in older engines often resulted in wet seals...who knows, oil type/brand arguements are old as time...
I run rp synchromax in my 5 speed- it actually fixed a balky second, and gotta vouch for it...but i'm chicken to go away from motorcraft 5w20 semi... always heard of excellent engine life in the 4.6, so just no real justification for me...I do think a 'frantz' oil filter(and no more oil changes) sounds like a pretty proven system- especially in older cars with conventional clearances/oils...still a little iffy on the extremely tight fitted 4.6 and its water thin oil...staying with recommended here for now

 

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