First post so be gentle! :)
I've just bought a 1991 998cc Mayfair and have a few "niggles" to sort out. First up, the sliding heater direction control (the one which selects "Screen", "Car" or "Off") jams and doesn't move smoothly between positions. It's kind of stuck in the central "Screen" position at the moment, if forced it will go to "Car" but it feels like something has dislodged and is catching. Maybe a seal has come loose, etc? The windscreen mists up quite badly too, regardless of setting (and no, I don't have modern expectations of the heater! :) ).
How hard is it to access the direction control mechanism? I'm hoping it doesn't involve removing the heater box entirely but fear it will!