Let us help you make sure this is what you need to fix your problem pump
Are you sure you need a new Unloader?
Don't Guess
The most common failure in these pumps is the check valves damaged, from the jet valve sticking in the head.
If that is the problem then get the newer version head without the unloader.
How to check if your unloader is good or bad
Unscrew the top brass knob off and see if you can move the stainless steel piston up & down.
If you can than your unloader is not the problem.
Also, look for O-ring protruding from small hole on side by threads
If it is then the unloader is bad