As you know Pete I've only just bought my 355, so not much insight to offer. Aside from the initial 3yrs, my car has been looked after by Migliore Cars in Bromsgrove. Really nice guys who specialise in older Ferrari's and Maseratis. Feedback seems to be very good and I used them myself for the PPI and to fit the Capristo exhaust. Overall I was happy, about rate seems to be reasonable and they seemed to go out of their way to keep me happy

My only gripe, they didn't fit the capristo exhaust properly, the solenoid that comes with it wasn't fitted and there is a slight blow where it meets the cats (that could be down to something not related to their fitting). By their own admission, they were stretched to get my car ready and rushed it, the honesty was refreshing!
My intention is to use them for servicing and maintenance, but anything aftermarket, I'll go somewhere else (although not sure what else I would do aftermarket?)
I'm actually taking the car down tomorrow to what would be my second choice for servicing and probably my go-to for anything aftermarket: SB Race Engineering in Aylesbury. They've been so helpful on the phone and have given me confidence they can sort my exhaust for me as they have done many before (unlike Migliore) Labour rate is higher, probably as we're getting close to London. I'll let you know how I get on tomorrow and if I'd recommend them.