This seems like a silly question but what is on your pump? The metal valve on the MW pumps are on the rear bottom of the IP, and it looks like the plastic one in the pic above the Govert posted for an M pump is on the top of the pump. Which do you have?

Just noticed the price of that shut-off valve in the link you posted $172.89!!!!!
You've got to be kidding me. I think the decimal point must be a place off. I'm gonna start snaggin' these mothers out of the junkyard for $1.50 and make a fortune.

__________________