Expert Advice on Impact of Changing to Mobil 1 Synthetic Oil at 98K miles on Toyota Sienna XLE Minivan?

I have always used QuakerState SAE 10W-30 (API Svc SM stds) on all my Toyotas that I change oil and replace with genuine Toyota filter every 5K miles, but I am seriously contemplating upgrading to Mobil One synthetic oil despite fact it is twice expensive like $30 for 5 quarts@Costco. My BIGGEST FEAR with 1998 Sienna XLE engine is maybe it has gotten too use to QS 10W-30 so I have fear that any new synthetic oil might affect the seals. FYI I did have my mechanic change seals on 1993 Camry LE later at 193K miles bec it was leaking oil when he did Timing Belt, Water Pump, Thermostat etc. Also I am contemplating adding via oil filler cap at various 7,500 mile intervals BG MOA � (Part No. 110). If I made MY BIGGEST MISTAKE though our Sienna engine runs fine, it was being too busy with elderly Mom in isted Living, helping 2 kids in MiddleSchool as until recent concerns about Sienna ATF, I was not aware that TOYOTA had SIENNA SLUDGE RECALL that I missed in March 2007 as we bought Aug 98