[cctalk] Replacement tachometer photosensors for RA8x drives?

I've discovered that three of my four RA8x drives (one 82 and two 81s) now refuse to spin up. All the failing drives give "SPIN ERROR" as the reason and I've discovered, by an combination of educated guessing and parts swapping with the working drive, that all three have bad optical sensors for the tachometer disk. Surfing around I see that this is a known problem. Apparently the compound that was originally used to pot these sensors turns opaque over time and, being as they're optical sensors, that really reduces their effectiveness. I've seen some reports of people trying to repair the sensors by either sanding off a layer of the epoxy potting compound, or even trying to dissolve it somehow, but that seems to be a little bit hit or miss. Doesn't seem like these should be hard to replace though. They're just an infrared LED and a phototransistor in a cute plastic case, and that technology is still pretty common today. Has anybody found a replacement for them? Does anybody have any suggestions? Thanks, Bob