Power Amp Repair - Bias Circuit - NPN Epitaxial Planar transistors

[gprutchick]

I am repairing power amps on a JVC FX515VTN. There are 2SD636 NPN Epitaxial Planar transistors used in the bias circuit. The bodies of these transistors have a hard white coating, looks like it could be paint. I am positive the coating is not thermal compound paste. I looked at an Onkyo power amp that that I keep around for parts. It also uses NPN Epitaxial Planar transistors (2SC1740S) in the bias circuits and these transistors are also coated in the same way.

What is this coating and what is its purpose? I assume it is some sort of thermal treatment.

Any help would be greatly appreciated.

Thanks,
Gary