Dropping charge between alternator and battery. Car won't start.

[M-A8]

I assume you still have the original black Varta battery with the sticker on top of it stating the part number 4E0.
If yes, then it's about the time for it to die so I wouldn't be surprise if it's the battery giving up and getting a new Varta or silver Bosch S5 will then more likely solve the problem.
If that's not the case, then you will have to wait for forum Gurus to reply to that and help you investigate this issue.

If you would have a VCDS cable and post a scan then that would help.