I've been happy as could be with my new/old MK9 purchase except one thing. The captured guide rod spring and guide rod tended to either protrude a bit and be off putting or felt a little mushy returning to battery like there was a bit of friction. Also, it has been a PIMA to reinstall the little bugger.
So, I decided to pick up the the Wolff MK9/40 recoil spring and guide rod kit. BEST DANGED THING I COULD HAVE DONE. No more hitch, no more protrusion and now easy as pie to reinstall. Here's a few dirty pics.
I had thought about installing a set of adjustable sights, but she shoots too good. They'll go on my p45 instead.