Not TR7 related but maybe slightly helpful!
I've stripped and rebuilt the whole system on my Golf, it had seized up causing the motor to blow the fuse. In an attempt to work it free as it was starting to rain, i stripped the splines. Not a good moment.
If the TR7 is anything like this then it's very straight forward.I had to force the shafts through bronze bushes, wrapping emery cloth around a screwdriver to clean up the bushes and giving the shafts a good clean before greasing everything up and reassembling.
The rear wiper on my 06 Beemer seized up too...
Rob.