I had the same happen to me & got the problem resolved.
The replacement Solenoid assembly came as a complete moulded unit (pipe assembly from lead-in, etc)...not separate bits as was on my shower, although I have had this a few years now, so maybe the newer G8000S units are slighltly different.
To continue, I also had to disconnect the Main Water supply pipe (Brass Joint),going to the Unit in order to get the Solenoid assembly removed. The small bakelite lead-in pipe was stuck fast to my faulty solenoid, but a bit of wriggling up/down, etc, managed to separate it...be careful..you need this part!
It was just a matter of putting all the parts back together, and thankfully it was a success.
Ricky Baird, February 2009