All the 4 nipple pumps are the same. Sounds like the pump pressure has been increased. The screw should be flush with the housing surrounding it. Compare your 'good' pump screw settings with the messed up one. Unfortunately, the other possibility is the pump diaphragm is no good. If your pump corrects the problem then you've isolated the culprit. I don't know if you can even get pump parts any more (probably not). You can try soaking the pump (assembled) in methanol - be sure the pump gets loaded with methanol. Lastly, you can disassemble the pump and clean the parts. Take the pump apart carefully I believe there is a spring in there. I've never seen an exploded view diagram of the pump internals (maybe somebody here... Bax?) can help; so you need to be sure you can assemble it correctly. I probably have a used one (or more), but can't guarantee the condition.
Good Luck,
Will B.