Small world! I'm fairly certain I bought it in the sales in the winter of 1993/1994 just before I moved house in 1994. It was advertised in the shop window and I think they were being sold off really cheap and I spotted the price and thought.. why not?
Here's some initial pictures of the pump. I'm afraid I didn't take very good pictures because I didn't know if this was going to end up as just another interesting/clumsy/damaging autopsy or a successful repair.
Note that there's a 1N4007 diode inline with the motor and this is only held in place with weak crimps and some heatshrinking. So this pulled/fell apart once I had the motor out. So I had to refit the diode.
Note that the shampoo motor was extremely hot when I took the unit apart and I don't think it likes being powered when it is seized internally.
So if you don't hear the shampoo pump running don't keep pressing the button as it will get very hot. I knew the pump was trying to do 'something' because I monitored the power drawn on an inline wattmeter and the power went up from 950W to just over 1000W when the shampoo pump button was pressed. But it made no sound so I assumed it was dead. But it was just seized on a bit of limescale inside the bore
Hope the internal pictures are interesting to GMB and other owners...