Stripped thread oil sump

[Fred Byrne]

I have had an annoying oil leak from my sump for some time. I decided to bite yet another bullet and sort it out. I assumed it just needed new sealant. However, when reassembling it to the engine I discovered the front long bolt had stripped the thread on the engine block. There are two strange things about this, first of all by some extraordinary chance it was the last bolt I refitted and it had come out of the same hole that I was re-inserting it into. What a fluke!! The second thing is why was the bolt hole stripped in the first place. I hadn't noticed anything untoward when I was removing it.
The problem now is do I drill the hole out and fit a larger bolt which costs me nothing (virtually) or do I buy a helicoil kit at a cost of £40 approximately and repair it so preserving originality. If I drill out and tap, it would probably be 3/8" BSF as these are slightly smaller in diameter than 10mm.
What would others do