Think I figured it out... the simplicity or stupidity -haven't decided yet- is astounding. Replaced the part and couldn't remember which end the eccentric went into. Compared wear marks on the other two pistons and installed it to match. Didn't seem right though, so I installed it the other way round and immediately noticed the pitch looked much straighter. Drove over to my indie who happened to be working on a 240D manual with the panel off, climbed under to take a look and indeed confirmed my instincts were correct.

The original part (likely replacement) when I bought the car was installed incorrectly. It broke, and my first replacement (being unfamiliar with the car) was installed to mirror it's predecessor.

Well, to anyone searching the archives, make sure the eccentric goes into the side with the indent.