I once did a Grundig, which evidently was brought back from a post-war US Army PX in Germany (since it was good for either 120 or 220 volt, switchable, and the labels were in English).

Anyway, the capacitor size/rating markings were not decipherable to me - nothing like U.S. caps. And, the schematic didn't help much either. I wasn't even sure of the polarity markings on the caps, red and green as I recall. As luck would have it, the radio worked fine without replacing any caps, and I have since given the radio away to a relative.

Can somebody steer me to a guide for German cap markings?

In the German radios (Telefunken,Grundig,etc) I've worked on (mid-1950's-1960's) the caps were marked standard to the USA value 'system'.

I've worked on scores of mid-50s German sets: by Grundig, SABA, Telefunken, Graetz, Blaupunkt, and EMUD, and I don't recall having much of an issue with cap markings. The tubular ones are generally marked the same as USA caps, with one exception: German sets use the term "nF" for "nanofarad" meaning 10^-9 farad where standard USA notation is microfarad (uF) or 10^-6 farad; or picofarad, or "pF" meaning 10^-12 farad.
A 3000 pF cap would therefore be the same as a 3 nF cap.

Most German radios (except for the SABA autotuners) use a nearly identical tube lineup, and most of them use two 50uF electrolytic caps in the B+ filter.