Just replaced with an almost identical new one. My son (user) reports that it leaked mainly from the main thermostatic valve assembly. It looks like the rubber seals were leaking which can easily be replaced. I suggest the whole unit is dismantled and descaled by soaking in vinegar, then any perished rubber seals replaced, and then the unit should be as good as new. The thermostatic part works well, so the leaks and scale were the only reason for replacing it. You will obviously need a few tools like adjustable spanners and hexagon (Allen) keys.
I can email you the assembly instructions from the new (almost identical) unit (from which the last image came (schematic).
Thermostatic shower unit (leaks and scaled) (Hove Park area BN3)
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