The original V series Nautel transmitters have required a couple of firmware upgrades in some cases.
The first was for the controller to add a little bit of bias to the PAs during analog operation. The second one I have had to do is to the PA modules themselves which was to keep the power supplies from shutting off during re-transfer from Generator power to commercial power.
I have done several of these and once you get the hang of it, it only takes a few minutes to complete. Still, I remember when transmitters didn’t have firmware. The low voltage control circuits were either 120 or 240 VAC with big relays and contactors that loudly confirmed their closure before any meters began to move.
Regarding Nautel transmitters in general; the newer models are not same rugged, reliable designs that were common in the past. We have AM ND series transmitters that have been on the air for 20 years without a single failure. The models rolling out of the factory these days often have switching power supplies fail without reason or warning and RF pallets that are fragile things. Ah well, I suppose all things are cyclical.