Leaky Diverter Valve on Valiant 831 eco plus?

Hi All,
I have a Valiant 831 eco plus (which has been nothing but problems since being installed 5 years ago).
Anyway - the newest problem I have was initially the pressure kept dropping on the boiler, and I have just recently seen that the diverter valve is leaking.

My question is - I have ready that Diaphragm kits are not available for other models in the Valiant range, but is that the same for the 831 eco plus?

And if not and I have to shell out for a new Diverter valve, I was wondering if someone could advise of correct steps for removal, as despite being quite technical, I am worried that if I do things in the wrong order I may cause more harm than good.

Thanks in advance

Laurence