The only vintage yamaha that has had spontaneous failures is the YH1000. I should say consistently has failures. I have fixed one YH100 that was said to have just stopped working but when I opened them to fix them, there was a clear screw driver hole through the diaphragm - modding gone wrong and failure to admit doing so.
The most recent pair of YH100 that I sent off after I tweaked sounded astonishingly good. To give you an idea, if I had to give up all my headphones and live with only that one, I would have been perfectly fine with the prospect.
As for modern ortho's being semi-DIY , I would disagree. Audeze and Abyss have gone high tech. Hopefully their investment in the field will pay off in the long run.