Thanks for the info Justin, its a small world, I have had the exact same problems over the years with venting tank caps and plastic bags. I also had the driver turn off the fuel shut off( above the tank) and it sucked the rubber right out of it.
Back to my S4S, it is a rotary pump and i think the problem may be in the primary pump assembly. There was air in the lines when i bled the system. the customer has not complained yet, but it is still Monday morning and anything can happen. I appreciate your advice
Thanks