Spray them with wd-40 or something of the sort and let them soak overnight. Then in the morning put a good quality allen bit on a breaker bar and hope for the best, if the proper metric size has gotten sloppy from removal attempts sometimes you can tap a standard size into the bolt with a small mallet. Either they will come out or they will strip out if they strip. You'll need a dremel tool, some oil and a small diamond burr or carbide cutting bit to split the bolt on either side to remove it in 2 pieces. Good luck and hopefully you don't need the dremel.
While WD-40 would be better than nothing for freeing up your bolts, something like Liquid Wrench or Kroil would be much better at doing this. And, assuming you get the bolts apart, be sure to grease the threads well when you put things back together.
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