Communication has 0 to do with the brushes. CAN com is to the UDC card only, regardless of brush, motor, or encoder conditions. Check for 60 Ohms across CCH and CCL with power off. Assuming this is TAC 32 hydro, CWIL card could have blown pico fuse, CPUA Could be shot, IOD could be shot. Personally I am leaning on IOD.

I believe the CAN comm from UDC is on Con 3. Worth verifying that it is wired properly down to CWIL card in COP as well. The CCH/CCL is very very easy to corrupt with induced voltages. Look in COP and make sure things are neatly separated, may need to do the same in the door operator, have had the 3 phase AC motors corrupt door communication as well.

If it's still kicking you without mercy, PM me. I'll get you my number so we can chat.