My brother has one of those Puch taps, it seems to work nicely. Of course, he doesn't use his bike as much as mine... well, in recent years not at all
Anyway, there's also a difference between original taps, and aftermarket and what's more you can add the varience between good and bad aftermarket. I have a cheap aftermarket tap on my 251, and I also have difficult problems trying to stop the plastic cup skipping threads... I also have used some ptfe and stuff, but yeah it's really difficult. I've got no proper solution to it that will work if I want to remove the cap again in the future