I tried taking the spunding valve apart, but taking the screw out at the end didn't seem to loosen anything up so I cleaned it real good using a pressurized keg of oxy clean. I hooked the gas out fitting to the keg, put the keg on it's side, covered 3 of the 4 holes on the spunding valve at a time and turned the pressure knob until water spurted out with a good amount of pressure. repeated the process, covering 3 of the 4 holes until I ran a good 2L of cleaner through the valve. I then did the same procedure with pressurized clean water.
Then I used the spray nossle on my air compressor to spray air through each of the spunding valve holes...I did this with the spunding valve all the way open.
The thing is clean as a whistle and back to accurate.
I didn't clean it well enough the other few times as I noticed that the spunding valve would hiss, then quickly stop, and then build pressure way above what I set. I would just touch the pressure knob and it would start hissing again...