I have a 1980 Honda CX 500, this year I pulled the motor out and replaced the stator so I had to replaced the rear case gasket, if you don't know the CX 500 is a transverse flying V design, water cooled motor, not like the Wing but getting there, anyway I was using Rotella T 15-40 with no problem but I recently changed to the synthetic 5-40 and I have noticed some oil weepage from between the front case gasket that is the original. Looks to me that the synthetic will creep past old hard gaskets much easier than dino oil from my observation, it may require me to pull that front case off and replace that gasket, so far no other issues, if anything the synthetic is washing out hidden pockets of sludge from clutch wear.