The 420 is not built to be serviceable. Basically if anything goes wrong, Centerflag's answer is to send it back in for service. The 201, and other adjustable Hyperflow regulators are designed not only for reliability, but also for easy field service which can be important in a tournament environment.
Taken from Warpig site. Comparing the 201 model with the 420.
I would speak to whoever imports them, and ask advice on it.
f not, remove the thing from the bottle (make SURE, its empty before you do this) and see how it comes apart. Probably dismantles from th eother end (inside the tank)
Gaz