can you post a picture for me? I feel like I am doing surgery in the dark? Now I will assume that you are seeing this:
If you take that whole brass valve of you will see a washer and a gasket like this. This is a pic. of the bottom of the water tube, but the top one looks the same:
Now if you open up the valve, you will see it has several parts inside:
and one of them will have a silicone puck:
Now with regards to your pressurestat...Does it ever turn off? Can you pull up on the bottom of it and hear it switch off.
It is adjustable, but I would only do this if you have a pressure gauge and can ensure you are setting it withing safe bounds.
Now please keep in mind, that I am giving you these hints based on my own experience. I make no commitment that they will work on your machine and I take no responsibility on whether they will or will not work. Any work you do on your machine is done at your risk. If you attempt to make adjustment to your machine, please understand the risk of electricity and the risk of damaging an expensive machine.
I would suggest that if it is not a simple fix that you feel is well within your mechanical skills, that you send it to one of the professionals that I referenced earlier in this thread.
Good Luck