You have Nikasil cylinders? On a 750? So I guess you had these coated, they aren't BMW are they?
Synthetic oil will often leak in places that Dino oil doesn't. If nothing else the Dino will leak slower. Many riders do want to use Synthetic oils but they cause problems in many areas of an Airhead. You should research before making any changes to Synthetic. We actually get along fine with the old fashioned Dino oils and they are more digestible.
There is a most controversial subject concerning engine oil. The Old Line is that engine oil needs ZDDP and you don't get it in Synthetic. However the leaks can usually be stopped by replacing all the seals and some riders do use the modern oils.
I use only Dino oils.
If you have a fatter tire on the rear there is a longer top hat spacer that sometimes will keep it from rubbing. I'll try to look up the part number later. (I think this works on a /5. I have the longer spacer on a /6)