I mistakenly said in post 11 that the 1/2" washers were the ones to get. They'll probably work, but the ID is on the small side for the 14mm plug thread - fit to the plug will be very tight. Sorry for that misinformation.
The ones I have been using are the 5/8", which I posted the link to in post 13. (They are also the perfect fit for the M14OS (oversize) thread plug.)
M14 thread OD is 0.56". The 5/8" washer with webbed ID will fit onto the M14 plug, and the webbing will hold the washer onto the plug when the plug is out of the pan without the interference of the washer rubber (webbing) to the plug OD being too much.