another bolt focc-up ideas?

[Val]

Hello,

I have tried to add new rad cover. 3 bolts have untighten fine. The 4th one - another bolt foccup.

First the hex key has twisted like spaggeti  :eek , the second 4mm hex key bit I just bought from Halfords has drilled the bolt  :'(

See pictures. Any ideas how I can fix that? I have applied industrial amounts of WD40 and penetration fluid before the final attempt to no avail.

Do I need to go to the nearest machinist shop for help?? Is there any easy way to unscrew that bolt?

Note the bolt goes into the side of the radiator which looks to me some sort of hard aluminium alloy, the bolt is steel. It is tighten so hard looks like melded.

EDIT: just reading some horror stories aparently steel bolts can be fused with the aluminium through galvanic action. Seriously guys?  :wall