Stripped thread oilway blanking plug

[GK5268]

I had a similar problem a few years ago, oversize brass plugs are available from suppliers, I did the work with the block in-situ and carefully re-tapped the hole, I used grease on the tap to collect the swarf and it was a success, but there is not much room to work with the block in place, but with care it can be done.

As a temporary fix, you could use liquid PTFE and just glue the plug in place, you would not need a fibre washer, so might get an extra thread to hold onto, once cured, it should be firmly held & should not leak.