Issue has been fixed!!!
There were a few issues going on here...
Air Down The Velocity Adjustor
Replaced torn 007 o-ring in the velocity adjustor in the HPR.
Air Out of Top Grip Frame
Took out HPR bonnet that attaches to the body. Replaced the 611 o-ring with a 012 (I had no 611 o-rings).
Also had to replace both the 017 and 018 o-rings too, as air was blowing down the top of the HPR.
Marker Not Cycling - Puffing Instead.
Replaced the diaphragm.
I also serviced the HPR - re-lubed it all. Unfortunately no DOW55 yet so used Smart Parts Greese (looks like Dow33).
Aired up the marker and it is nice and snappy. Unfortunately, for some reason my chrono isn't picking up the reading when I shoot re-balls indoors. Not sure why - in a light room though. Was fine last night when I was testing my Empire Sniper out with the reballs - but was in a different room..
I am on-call this week, but will nip over to my local site and try some paint and their radar...
But PHEW - I have learnt SO much about this marker and I am GLAD it died on me, as now I can fix it in the field