Thanks, Ray - that's a kind offer. I was stuck for a while in Brodick and missed your post, so whiled away the time giving it a go - managed to access the wheel drive once I'd worked out I needed to take the wheel off..! The pop-fitting on the grey ring was stiff, but access to the motor through the instrument pod was an exercise in spelunking. Still, at least I now know that the motor is kaput! Perhaps it's time to upgrade to their newer unit...
Dawntreader, apologies for not making that clear, and thanks for your suggestions. I'd not even realised that there were different types of wheeldrives!