Yup, that's exactly the partI was thinkinbg of. It's basically the same type of valve. It's not connected in the oil passages. I won't say that a truck or car engine can't/won't have one, just that the assembly and shop manuals only call for them on the van models.
On to the leak, check the filter ling and gauge line fittings, one may be loose. Also, check the hoses and the gauge line itself for cracks.
