I spent a few hours looking for a 3/8 check valve I could put inline between lift pump and filter. Most were aluminum which can corrode. Others were bulky.

One link mentioned that the overflow bolt on the Mercedes diesel was actually a check valve that was intended to help prevent long cranks by preventing fuel to return to tank.

If so, maybe I just need a new overflow bolt. Some threads say some bolts are rebuildable but spring can't be ordered just stretched.

Is this pretty much the way it is?