It hasn't quite worked out

- probably because I've been impatient.
Don't laugh at (or scold) me - the gentle approach of repeated application of tiny quantities of a penetrating oil and constant movement of the door yielded absolutely nothing. I eventually resorted to some watch-repair type tools (toy hammer and various drive-pins) and very gently tapped the hinge slide-pin back down in to the door. The door was wiggled and out it came - an apparently good result.
The down side - the pin was pushed tight to the other end of its travel in the recess and, despite best efforts with a bit more penetrating oil and application of force through the end of a flat blade screwdriver, it would not move back to where it came from!
I've had to butcher the door by filing away a small part of the 'tube' at the hinge end of the door in order to gain some purchase to tap the hinge-pin back out (partly at least).
I'm not convinced even if I had shown some patience and let the penetrating oil do some work for a couple of days that I would have avoided resorting to such drastic measures on a relatively delicate, simple mechanism - I belive it was pretty much FUBAR before the camera came in to my possession . . . . . and it certainly is now. It will ever operate as the manufacturer intended again but should, hopefully, not need to be removed by the 'tap the pin back in' method for a long while after its reinstalled.
Now all I have to do is rub down the flaked paint and rusty steel, apply some rust inhibitor and apply some black paint - at least the film pressure plate popped out easily
. . . . all because I want to change the light seals

I don't get this hassle with my (forgive me) 450D, but neither do I get the satisfaction of collecting 38 or so 'real' photo prints.
Sorry for the essay above. Regardless of my little misadventure, your comments have been helpful.
Thanks,
Gary.