I had a stripped thread on the crankcase where the clutch cover fits. Not having a huge amount of mechanical expertise, I was inspired by Nurse Julie's posts, and others, to have ago at sorting it.
I bought the bottom end of a 400/4 engine from Fryerk (cheers Kevin) very cheaply, and had a go at a helicoil on this before trying on my bike. The helicoil turned out to be pretty straight forward.
The stripped thread was accessible without taking the engine out. I took the clutch cover off, and had a mild panic as the kick start shaft came out with it, but pretty straight forward to relocate it.
The helicoil was straight forward again, as my practice run. Put a new gasket on. I read the different views about grease/no grease, and decided to put it on dry. Had fun and games initially getting the cover back on as the kickstart shaft was not fully seated, but once I'd sussed that, it went back together. New filter and oil, and Bob's your uncle. A very satisfying few hours thanks to the excellent advice on the forum.