I had to drill one of mine out in the end. And then replace the mount with a new one because even with the bumper off, I couldn't get the left over bits out of the mount!

I replaced my Torx bolts with some marine stainless ones I got from eBay.

I got some normal hex head bolts but with a flange around the head for a couple of quid and they're doing an excellent job so far....
 

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