On the right side of the machine is the slotted cover that protects some of the pump head and pressure switch (black box). If you take the front of the case off, you can remove that cover and gain access to these parts. Check the bolt and nut as shown below (from Comet): 
If that nut has broken loose, or if the threading on the bolt is no longer keeping it in place, look at this fix from one of our customers that may work for you:
I ended up finding a stainless nut to put on the other side of the bracket and it works perfect. While it may not be the most elegant, it seems to be a solution.
Unsure if you want to relay this info over to them, but I think the proper procedure would be to turn the nut counterclockwise to free the threaded shaft. Then turn the whole shaft clockwise to press it further into the momentary switch. Once it was in the right place, then tighten the jam nut back into place.
I think what happened was that I turned the nut clockwise (without first loosening it), which caused the thread to pull against the soft brass and stripped it.
Alternatively, if the nut is still securely in place, you can use an allen wrench in the end of the bolt to adjust how far it inserts into the pressure switch. You may need to experiment tightening and loosening to find the right position.