Yesss, metric helicoils and M 5 - or M 4 screws for that place. Stupid to go for obsolete BS , who cares in a few decades anyway ?? And no question about helicoils, they have been great for many decades provided you do them right, meaning drill with lubricant and correct size, plus thread cutting with lube. Should be no question but reality in work sheds can be otherwise. Helicoils are standard even in new production when there is good reason. And certainly hundreds of millions, a multitude of numbers from imperial , of European and Japanese machinery got metric fasteners - and they keep together better than British . . . .
Now, even with imperial, seems they don´t last for decades , so obviously some need for repairs ??? Another reason for me to go metric is the wide choice of screw types, unlike imperial, when you just have to accept what you get - at ridiculous money - plus brexit nuisance. Life is too short to mess around with imperial fasteners when there is an easier and practical alternative.
Actually, in my case I plugged the old threads with alu threaded inserts as the positions did not fit the clutch cover, so no helicoil would do. So no heliciol here, but in most other places for sure.
Vic