Update re. the shift issues that I described at the start of this thread. I got the car back today from Tony and his team at Aston Martin Summit in NJ. They found that the ASM clutch fluid reservoir was low due to hydraulic hoses with slow leaks; nothing visible on the ground. Hoses replaced, under warranty, and the gear shifting noticeably improved, but still wasn't quite right. They did a test drive data dump for the AM regional troubleshooter and the consensus was that to get the car back to spec would also require a clutch change. 15.5K miles on the car, so this was not a surprise to me. The clutch friction plate wasn't quite down to the rivets, but the flywheel was badly marked up.

I spent a lot of time researching OEM vs twin-plate and understand the pro's and con's. As I have another 18 months of AM warranty and will have 12 months of clutch warranty, I elected to play it safe and go OEM this time.

The car finally, in my ownership, drives as it should, so I can now hopefully enjoy it for the Summer.

I have to say that I have been very pleased with the levels of service provided by Tony and his team.