Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
Or just a rounded cap head? Never known one strip, but deffo had to destroy a few getting them out. I have in the past reclaimed them, filing the flats to the next size socket. But it’s a tedious and unrewarding exercise and I’d be inclined to just replace it.
You should never try to remove these with a impact driver as, these are thin alloy and can crack. I must of removed thousands of these over the years. The early 750 had a 17mm head which was easy to remove then, Honda changed them to a 14mm head making, them more difficult to get a grip on.Heat the around the cap to 250 degrees to soften the o'ring and break the seal and use a metrinch socket which grips the flats
Not forgetting that any form of turning a seized gallery cap will cause further damage if it is the threads that are seized and not the o-ring surfaces