4 Tech Geeks only: ISO Opto Isolator Reccomendations

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I am an infrequent Talk Bass Poster so please forgive me if this question seems wacked....

I own a vintage Mutron III Envelope Filter.
The unit in question is probably the 2nd iteration of the original as it is hard wired with a power supply. I used to own an earlier version with the weird 3 prong female power input that required and external supply, but I sold it after buying this pedal.

Anyway, this thing has been gone through and all the IC's have been replaced. My friendly neighborhood repair man suggests that in all likelihood, the reason this device has ceased to provide it's notoriously famous creamy envelope effect is that the opto isolator has crapped out.

The part in question is marked "805A 8J" and the schematic I have for this pedal says "0805."

I am wondering if any of you technically minded pedal afficianados might be able to provide me with a link to a reputable source for one of these?

Any help would be appreciated.

Thanks!

Grateful Ted
SF, CA