Me again....
Given that R26 has gone a bit high (2.53K vs 2.2K), the best replacement for C27 would be 56 ohms. If you replaced R26 with 2.2K an easy approximation to 51 ohms is two 100 ohm resistors in parallel.
So far as the capacitor check with battery and meter is concerned anything more than a few microamps is bad news, so any current reading at all on your meter would be suspect.
FWIW I use the same meter for my "so cheap I just chuck it in the toolbox" meter. (I think the last offer on them was two for a fiver or something similar). It's actually lasted several years so far and seems OK.
Doesn't it have a transistor check function? The small round black socket on the left, used with the switch set to hFE. I wonder if it will cope with a germanium device's leaky nature compared to silicon? I feel a quick fiddle in the shed for curiosity's sake coming on
Dunno if I've got any OC81s not in sets but I'll try something similar.
Just spotted reply above... when the current is at zero on the 20mA range, try switching down to 200uA (two clicks anticlockwise) if it's still zero or a few uA, nothing wrong with the capacitor leakage wise.
Chris