Simon / Peter
The fault with the cockpit drain affects the D365 as well. When got ours 3 years ago i overhauled the autopilot rotary drive. The chain sprocket was corroded down so it had no teeth left , and as you say it then got into the motor drive. It took me 5 hours with a dremmel to get the socket off and about 20 hours to repair the motor drive
I simply plugged the drain hole from the inside with silkaflex and live with the 2-3mm of standing water instead.
The factory fitted rotary drive / chain works really well apart from that drain hole