Can any one help with any information on these units. Can you open them up, if so how.

I remember doing this on my '87 9000T, but it was a long time ago. I think I just prised open the housing and glued it back together afterwards. I opened up the motor inside (not intended to be opened) and cleaned it up, which got it working again. The motor itself, or one like it, is probably available separately from somewhere.

Why bother when you can pick up a replacement at Maplins for a tenner?
I've spent many a happy hour drilling the rivets out and packing mechanisms to get them to work, but the Maplins replacement is an easy fit (may have to adapt the wiring a bit) and works for much longer!
Pete.