I don't know. I have seen the definite cross thread, wrong thread including 1/2-20 dire on thread extreme overheating (case melt) etc. But let's get back to some basics. Most over tightening is the result of "it is leaking" so tighten some more. From the engineering perspective  all threaded fasteners share common principals. In order for them to stay tight the process of installing requires something to be elastic enough to compress, or go into tension  or otherwise deform and remain elastic to maintain tension on the connection that is above all other loads. Think of a door chock. So for the oil plug over time something has to give, hopefully it is the washer. Also for this application the washer has to be correct size. If too large it does not fit properly into the step-recess.  

Dennis

-----Original Message-----
From: Roy Nicholl [mailto:RNicholl@NBNet.nb.ca] 
Sent: Sunday, September 1, 2019 11:34 AM
To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Cc: vanagon@GERRY.VANAGON.COM
Subject: Re: copper crush washers

> On 01-Sep-2019, at 11:30, Dennis Haynes <d23haynes57@HOTMAIL.COM> wrote:
> 
> Since I have repaired many stripped plug threads I'm not convinced the copper or aluminum is the best choice for this application. 

How many of those are the result of over-tourquing regardless of the washer used?