I don't really know the exact specs for compression on that motor , but I would guess it between 450 to 475 and no more than 10 percent difference between any two cylinders , you will need a diesel compression tester which goes higher than an automotive set up and an adaptor to either go thru the injector holes or thru the glow plug hole , if your motor has glow plugs and not a intake warmer set up , which I think it may have , if it has glow plugs for the price of one plug you can make a adaptor -------------------------yes the washers will let air in and it will leak down over night or quicker , and you don't see it leaking externally , I have replumbed a couple of Takeuchi's which uses that same filter housing , to a regular style filter housing as we were always having trouble with those banjo fittings , did you ever find a plastic screen in the banjo fitting which sits on the inlet of the hand primer , a clear piece of plastic tubing , if you can plumb it into the fuel line right before the injection pump can help to see if air bubbles are flowing thru , I think you mentioned fuel in the oil , another way it can get there is the seal on the end on input shaft of the injection pump , ---------------- 3,700 hours is alot , but if it was properly maintananced I would think it would go over 5,000