mxslick.
Thanks for your valuable advice. I've done some partial disassembly. There is an unloader valve, but it's not like any I've seen, the actuator works off the pressure-switch mechanism, so its vent is into the switch housing, which is coated in oil but perfectly preserved! The motor/pump is inline, direct drive, so I'll get unloaded readings with the cylinder head off. I'll post before and after/detail pics when it's renovated.
Thanks again,
Alan.
