I guess I am a little biased as I am a Amsoil dealer and run it in every thing I own cars, trucks, boat and now my 750. The Harley and Beemer boys love it. If mobil or castrol syntec is your brand that's great, most syn's offer better protection than the best dino oils.To those that get xxxx miles on dino oil thats great but is not the norm, very high milage and abuse with no problems with syn is the norm, not exception. Not knocking anyones choice here just my observation. As to syns worsening leaks, it is possible, if you have sludge buildup on a seal or o-ring it does not keep getting conditioned by the oil and dries out. When you put in syn the additives eat away the sludge exposing a leak.
If you already have a leak you will still have a leak with syn but oils like Amsoil and Redline have a high amount of seal swell additives which if the leak is small it may repair itself. Also some of the high milage specilty oils have the same conditioners in them. Syn viscosity is much more stable and resistant to temp changes which cuts down or eliminates clutch chatter even in cold weather without long warm up periods.