Thanks Pitman.
Replacing sum clearly the best long term option, but very messy on my 1.6 petrol as it's boxed by the exhaust, so I really don't fancy removing that with seized bolts!
Looking around the web it seems a common problem and even main dealers doing it! As said, the softer sump material, it's always the thread not the bolt that damages.
I'm looking at a few different options. Quite a few have helicoiled, but just seen something else that might be a good solution. Just going to email them and see what they think and will report back if it's a prospect!
Wow, these guys are on the ball...
Emailed Femco and they rang me within 5 minutes. This now looks like favourite solution:
compact drain plug
Basically, I can buy from these people a plug of the same size and thread and fit it using a permanant thread bonding compound.
You buy the drain plug with a hose and future oil changes are simply a case of attaching the hose to the drain plug and running it straight into a tub. No mess, not bolts....
Seems a runner? Total cost is about £40 delivered with the additional hose attachment. This is a bit more as I'm looking at the compact one which has a low profile, so should mean it's not at risk from grounding.
To be honest, I might have fancied this anyway for future ease given how quick clean and easy it is.
Any views??