I've just re-read my post and I forgot to mention that the first time I tried to depressurize, the rear went down completely but the front never moved at all.

Does this point to a solenoid?

just fitting that replacement block and see how we go from there.

Bit of a cock up though. there wasn't a driver pack with it so lets hope it's not that.

Anyone know which way round the wires go for the pressure switch, or does it not matter?. 2 red ones.

Doesn't matter, it's a simple on-off switch. Make sure you give a good squirt of contact cleaner into both multiway connectors before putting it in.

so the new blocks leaks like a b*d. I've moved on to stripping down the original.

Should the diaphragm be in 3 bits??? I don't recall it was. Looks to me like the metal cap has bust off.

I think you've just found your problem......

indeed. Stripped the new block ive just bought to reveal a shiny new aftermarket one. Happy days!

Fixed.

Flippin diaphragm. It was a new one too. Methinks I'll be sending an email of disapproval to the seller.