Pleased to say, that seems to have done the trick! New dessicant in today and hopefully all good for another year...

Well I rebuilt the valve block, didn't look too clever in the NRC area for sure. While I was doing that had it all pumped up on manual air valves and no droop at all in 3 hrs. When the rain stops I'll do a test drive and see if it's now sorted...

I'm going the a very similar exercise myself. Did a full rebuild, o-ring set etc but still slow. leaks. Putting the block on the bench, hooked up to an airline with a tap and gauge T-eed in as below, I can pressurise each bag line in turn. Pressure up, soapy water, and the leak presents: It's...