On ones I have fixed I just drained the oil, cleaned area as best as possible, then tig welded a new 1/2" thick boss on.
The heating washer trick does work but not the way stated.
To be truly effective at reannealing(softening) it best to heat to cherry red with blowtorch, then drop in OLD oil, otherwise just leave to cool, used to do this on 2T bikes years ago, worked every time.
I don't use any washer, I just put a sealant on the threads, wipe area next oil chage you will see it spotless, doesn't leak one drop, but on non alloy sumps it can be useful having it covered in oil as it stops it rusting like my astra!!
tabetha