Simple question I almost feel dumb for asking but want to give as much life as possible to this older compressor. Basically, is the oil checked with little square dipstick screwed in or just seated. One way is below the hatch marks and the other is overfilled so I feel that its pretty important. I've looked everywhere for owners manuals and tried to compare to similar pumps but have had no luck. Any help would be greatly appreciated. Seems like modern compressors have actual dipsticks that are much more obvious in their use. Thanks in advance.