Modern Vespa

I'm trying to remove the two star headed bolts that connect the rear carrier to my GTV (or GTSs too). One came out after putting up quite a good fight, but other won't budge and i fear i may have rounded off those little stars inside slightly. Does anyone have any tips on getting this final bolt out? Are there replacements avail if i have rounded it off and are they worth replacing with allen key ones? Thanks in advance.

I have found these extractors very worthwhile, good luck. Made by Irwin or Proto, most pro trucks Snap-on and Mac, etc. have them.

stars bolts suck ass IMO. if they round out drill the head off, remove the rack or whatever and then you can see the threads, spray some penetrate let stand for a bit and use a set of vise grips to remove the rest of the bolt.
Replace with a allen head style bolt.