Ruined thread on wheel hub

Hi all, haven't posted for a while as the cabrio has been dry stored and I'm not getting it ready for summer  8)

Took it to my local tyre fitters for a new set of boots and the previous owner had used a non-VAG bolt in one of the holes, tyre man took out the bolt to discover that the thread in one of the bolt-holes has been destroyed   !

I can't get a bolt to torque up now, so my NSR wheel is only held by 3 bolts. Is this safe/legal/an MOT failure?

Any suggestions on a workaround or will I need a new hub?

New drums, shoes and wheel bearings should sort it out. I am surprised the thread within the drum has been damaged by an errant bolt, the only thing I can think it would be is if someone cross-threaded it?

or ran a different bolt type though it. usf and metric. they look close to the same and you can start them both in the same hole but will need more and more force to tighten them in. (breaker bar and a monkey) might be able to get it helicoiled but for peice of mind i'd change the hub on the front or the drums on the rear as paul has said.