Zeal
If I had problems passing your check ride for a number of years, I think I wouldn't be showing the zeal as you put it: but that wouldn't make me any less determined.
Obviously he needs to concentrate hard on the parts of the test giving him trouble: he has got far enough to get to the tests so one assumes he has made some progress and can at least handle an aeroplane?
I think changing instructors is the logical choice-even if just for a few lessons. A fresh pair of eyes can usually pick up all manner of things. Even if it is just a few hours with a different guy, they might be the wisest investment in his aviation career to date.
Encourage the man. He may need a 'talk', just not the one you proposed!