On Sun, 17 May 2020 21:06:23 +0530, Pimpom wrote:

I used to have some OC71s and OC72s a long time ago. They made neat
phototransistors with the paint scraped off from their glass
enclosures.

OK, I got the AC188s. With a DMM they measure 25-50 ohms forward and a
few Ks in the reverse direction.

I think you've misunderstood the problem here, Pimpom. The leakage in
question is between the case ("screen") and the die and significantly pre-
date the black-painted phototransistors we all fondly recall from 50
years ago. :-)