Hi guys,
A fascinating discussion on drain plugs...

Just to throw something else in the mix, my 2007 crd has a 3/8 thread on the plug. After trying metric plugs & failing, I let it be for a while & used the old plug with new washers. I eventually sourced some excellent quality stainless steel plugs from China.

Hope this info is of use to someone. I used a copper washer as well as the flourine rubber gasket that sits in the groove.

https://www.aliexpress.com/item/1005004 ... f19cuAQhaw