We received a helpful tip from a resident who recently replaced their shower mixer tap following problems with temperature control and pressure.
"The cost of spares and the work involved in fitting innards for the Grohe mixer were such that we decided to buy a new unit - a Grotherm 2000 NEW, which Grohe confirmed is a direct replacement. It is a better-looking design compared to the old one. We bought one on-line at a considerable discount to the Grohe price.
Fitting was a doddle: turn off the water supply (see here). Uncouple the existing unit from the wall - two 30mm nuts. Fix the new unit (a low profile ie, thin, spanner is required. Neither the pressure valve nor thermostat should require adjustment. Turn the water supply back on and voila.
There is a Grohe clip-on shelf or 'rack' for the mixer which fills at the space between the mixer and the wall, which can be obtained from Grohe".