Sounds to me like the threading on the outside was caused by vice grips
slipping. Seemed to work for the po.I would use the same tool this time,
and finnish them off. Get new bolts.Just dont know why VW uses so many
allen hex fastners. All over the Vanagon. A 8mm threaded shaft normally
has a 13mm head.Lots to grip on.But  no!! VW uses a tiny 8mm hex allen
wrench to remove 8mm threaded shafts.Of course , at times there is no
access for a hex head,but most times there isi would be very careful when
removing the same bolts from the blackcave..