Dear Don and Chris
Many thanks to you both for your helpful replies. I'll try to phone John Margarson and will post the conclusions of my discussion with him on this forum, and will also let you, Don, have any detailed information that he gives me. If this draws a blank, Chris, I'd very much like to borrow your plywood model - we could cross the Solent to pick it up - and I then know someone locally (i.e., in Oxford) who might well be able to make something similar in stainless steel, and this specification could then go on the Maintenance page of the website.
Best wishes
Gilliane
Miss Fidget, Super Seal 26, no. 69
Delphine, Parker 275, no. 41