Unless the car needs some specialist 'Morgan Specific' work I'd probably stay clear of main dealers.
I would absolutely agree with this - even for 'Morgan specific' stuff. Anywhere that has proper mechanics rather than than just 'vehicle technicians' or whatever they are called these days is perfectly capable of doing anything on a Morgan. There is absolutely nothing on a trad that would faze an experienced mechanic, and all the engine stuff is very straightforward.
I use a local independent to do work on the Land Rover and I get him to MOT the Morgan. He's always offering to do any work on it that I can't be bothered with and the guys there are always working on older cars. They even maintain a Hudson Terraplane for an old guy who lives locally.
The idea that a trad Morgan needs to be maintained by a Morgan dealer is a great idea for the dealers, but not so good from the owner's point of view.
Tim H. 1986 4/4 VVTi Sport, 2002 LR Defender, 2022 Mini Cooper SE
