I just put a slip on on my 950 a few weeks back. I don't recall having to remove a gasket. The stock clamp, yes. I got a Rush slip on, and like you had about 1/8" to go before it was flush with the back bolt holes. All I did, since it wouldn't go all the way by hand, was folded up my flannel and put it on the end of the exhaust, and gave it a couple light kicks with my boot. Voila, perfect, flush, no issues, no dents. It's just a super tight fit, which is totally fine.