Had a good look at the sump plug hole today - don't think the Doc's plan A is applicable.
It's a combination of a number of things -
1.. there is a chip out of the lip of the hole no much but enough

Taken before it was helicoiled - not as big but still some there
2.. the copper washer has to have a big enough hole to get over the thread of the sump plug but when it reaches the head of the plug there is a much narrower smooth section so the washer can move sideways quite a bit.
3.. A combination of the above means that the washer doesn't cover the nick and the flat on the head of the bolt doesn't cover all the inside of the hole in the washer leaving a pathway for oil to leave the sump
So it looks like - find a plug with a thread right up to the head so the washer can't move about and/or use the Doc's Plan B with plenty of goo under the head of the plug
_________________
David L
My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!