in the eighties whilst on holiday in Germany, I picked up an R4 with drive for a friend. I had 38 days before I left for home, so I gave it a bit of use.
I compared it to my F3 with drive which I had with me and found it to be alright, but not something to write home about.
I then loaded a couple of extra frames than I should have into a cassette, something like 39 frames instead of 36, (lost count of the revolutions). The R4 didn't like things when it got to the business end of the roll, basically it started to slow right down.
I took it back to the shop and explained things to the very helpful salesman. He took the drive off, took a drive off a camera in the window, swapped it and it was really a different machine with that second drive on.
I remember the salesman just rolled his eyes and muttered something about German engineering, smiled and wished me a good holiday.
What made me wonder a bit more about German engineering, happened a year later, when at the same shop, I picked up a 180 2.8 leica lens for the same camera. As I didn't have a Leica with me, the salesman loaned me a secondhand R4 to use for a few days to ensure it worked correctly.
Well the lens was so tight to focus, I figured the helices were either not lubricated, or the tolerances were unbelievably fine. Apparently the tolerances were very fine and I was assured the lens would be perfect in a few years time. I didn't think that was a really great thing, but it wasn't my money, so I brought it home.
The lens did loosen up in a few years and when it was about 19 years old and had done quite a fair bit of work I met up with my friend and we checked a couple of things out.
The R4 and drive are working wonderfully, about 500 rolls a year.
The 180 is still perfect and silky smooth.
By comparison my F3 is still going very strong, looks terrible, but works wonderfully. The drive still sounds as loud as ever, but works beautifully.
My Nikkor 180 2.8 isn't as tight as the Leica, I'm sure the helices have worn a bit, but it still gives me the results I wish for.
I would suggest that if your drive isn't up to the job, it may not have been the best right from the start.
Having owned fifteen BMW motorcycles and worn out 9 of them, I have seen German engineering at it's best and worst.
I don't think the Leica camera manufacturing would be much different from many other German manufactured things of it's era. Most assembly of manufactured goods at that time, was done by immigrant workers, with a reasonable amount of quality control things went right. I do though, in the pre computerised and CNC days, believe there was definitely Friday afternoon assembly days.
My two bobs worth!