Petroleum based after-run oils cause the silicon diaphragm in the pressure regulator to swell and operate erratically. Remove the regulator housing and flush with methanol (or just regular fuel) rinse both sides of the diaphragm. Put the regulator and parts in a separate ziplock bag until you are ready to run the engine. I would probably try to find another diaphragm to purchase, too. I would probably just replace the diaphragm right before you run the engine (and flush all the after-run oil out of it).
The good news is that the diaphragm is quite inexpensive and I think they are still readily available.
Get some Ultra oil
-Will