Good morning. I'm in a mood of distracted boredom, and thought I'd start a rousing games of "why'd they do that?", 'they' being the factory.
I have noticed on more than a half dozen odd Z's that I would say are relatively unmolested, that the six bolts that hold the wiper arm pivots to the cowl are quite surprising. Five are identical, one, the same one on every car, isn't.
Here we see on the left side, that the inner, rear fastener is a round headed machine screw, bereft of even a lock washer, while all the other five are nice hex SEMS bolts with the expected lock washer. All are of course M5x0.8 thread.
Right side, all is happy with three matchy matchy.
As those of you who have had the pleasure of removing this lovely flock of fettid fluffy fasteners have experienced, it is not enough that 4 out of 5 of the bolts snap off, but you have to resort to vise grips to get that lone round headed bastard, rendering its head beyond repair for future use, causing all sort of consternation and wringing of hands.
This was recently observed on 3798 (pics above) and on a 73, VIN 127xxx. Can't say for sure what other years I've seen, but a good sampling.
Let the speculation begin. Why in the world would they use one odd bolt in that group of six in such a systemic way? I think the assembler was a clever prankster, and revels in the joy of imagining the future angst he/she will have caused. Well congratulations. It worked.