I'm not sure what the compressor is, but given the fact the it will hold a vacuum and that the dye loss was centered on the low pressure fitting with an increase in concentration up to the fitting, I'm pretty sure that the compressor seals are okay. I tried two different tools on the stem and niether of them would fit over the center pin. if you look down the bore of the fitting, you can't see the crossbar that the valve stem tool catches for removal / installation. I'm not sure if this one has a replaceable stem, the top kind of looks like a ball bearing..