I used some paint´s thinner, R110 it´s the name. It is like light oil, but very strong and smell hard, but nice in the few seconds, I recommend to use dust mask with smelling filters. INSIDE? an array made by transistors, low noise I guess, maybe two fets, need to be sure, since no label or letters over devices, erased by AR people, looks like an op amp array, very similar to the mark levinson modules, I will work on schematic and the share with all you guys. One of my freinds told me he found an old round octal op amp in one o those modules , but I am not sure if it is a real AR module.
Anyway, I will try to replace the circuit by the LM4562 very very nice quality OP AMP used in many hi end brands as a secret weapon, limited only by supply voltage for this case.