As an outsider (and a complete EV convert and Tesla fan) looking in, I find this thread so disturbing..........
I could live with 100% DU failure of early cars with a new DU replacement and then NO (or minimal) problems. And few DU problems reported in later cars.
And continuous improvement in DUs so that newer cars and later replacement no longer had this issue.
But how can 2015 DU replacements still fail (in under, say, 100k miles)? Is Tesla just putting in (badly) refurbished old DUs one after the other? Surely doing it properly now is essential to get this issue to go away - it must be having detrimental affects by now on Tesla....
Maybe Tesla is really struggling to solve the issue and still hasn't got to the bottom of the problem. Why not?
As I have said many times - as soon as the DU issue is sorted then all replacement (and new) DUs will be 'bullet-proof' and the issue will gently fade away but this point sadly does not seem to have arrived yet.
This may be doing more harm to Tesla's reputation than to their cash balance as I imagine replaced DUs are relatively cheap.
It should be noted that BMW had a similar issue with their fuel pumps failing. It took they several years of study and redesigning SEVERAL times to get it right. But the issue has faded into the oblivion now.