I won a new VALEO 12v 55amp alternator off Trade Me Auctions recently.
It was covered in thick GREEN paint as it was off a new Volvo Marine Diesel. Yes it has a sealed comm ring.
I dismantled the unit completely and stripped the paint away then had the bits beadblasted to finally clean the surfaces. All the parts then were sprayed with clear laquer to seal the surfaces from salt attack.
When completed I had our Auto sparky run it up on the test bench as a final check. All OK.