Perhaps I should add some more information. The generator is a Honda E-3500 belt driven unit. The actual alternator section is manufactured by SAWAFUJI Electrical and the part number they use is E-3500 also and the AVR is part of the SAWAFUJI unit.

I would do two things.
Try to find the cost of a third party AVR that matches the original spec and install that on the generator.

Second is to find out the cost of an entire altrnator that matches the engine, ie, direct coupled, same or less real power (Kw) output, nominal power factor machine, that produce same voltage and the frequency.  I would also want to (or perhaps you can calculate)know the moment of inertia of the new alternator rotating parts, which should be closely match to the original in order to avoid any vibration and barred speed operation.  Of course the important thing is that it should have simialr physical dimentions for proper mounting and direct coupling.

try using a hot air heat gun on the potting material-
if it's a silicone based it will become pliable enuf to flake out w/a probe or screwdriver;it worked for me