Managed to get this sorted in the end. after drilling out I managed to save/retap about 60% of the thread. I put a bolt all the way through and nut on the other side to be sure. In the end the damage wasn't as severe as I first thought.

thanks for the replies, especially @jamesmartin & @neilly who took the time to reply in detail and keep the thread going.

This LR diy maintenance is a massive learning curve!