depends on the seals
I have experience with two Ford trucks using syn oil.
1. 1989 Ford Ranger 2.9L - Bought new, changed to Mobil 1 at first oil change (3K miles) Sold at 125k miles last year. No problems - BUT it did leak like a sieve (starting around 30 - 40K), especially from the valve covers which I replaced 2 times - 1st @ 50k , 2nd @ ~90k. Those gaskets were cork by the way which was probably considered state of the art in the 50's. One advantage of syn oil is that it is easier to clean off of the driveway
. Never any sign of oil burning, but hard to tell after 100k because of the leakage rate.
2. 1997 Ford Exp 4.0L OHV - Bought used @ 32K miles, switched to Valvoline Syn @ 36K miles now have 78K miles. No sign of oil leaks so far. No sign of oil burning so far.
My opinions based on my experience and knowledge/background:
Newer synthetics may have better formulations for seal swelling than before (probably true)
97 engine built with better gasket and seal technology than 89 engine (definitely true for Ford V6)
Loose engines may leak (and burn) more oil when using synthetics (true because of the molcular properties of synthetic vs. "natural" oils - the molcular chain length is more consistent for syn oil but shorter on average so they can squirt thru gaps more easily)
Conversely, tight engines will usually burn less oil with syn oil for the same reason (the super short molcular chains in "natural " oil will burn off quickly - and the oil will break down sooner than with syn oil)
The only vehicle that I would not use syn oil with is one that already had a bad leak or bad burn problem (too expensive) Otherwise I think that the benefits outweigh the downside.