Issue solved, the bracket the bolts go through is aluminium and the hole had got slightly damaged... luckily my welder had a nifty little gadget that used a sort of spring jacket that opened up inside and redid the thread inside

Did anyone ever find an off the shelf alternative? Cheers

Hi, I had to disconnect the rear heater system completely and remove it so the underside of Betty could be replaced. I've gone to reconnect it all up and whilst the coolant pipes have gone on fine, the two metal AC pipes just will not tighten, the bolts aren't stripped so I'm wondering; is there ...