oil check valve help

[soonerfish42]

I have a 1991 Bass cat sabre with a 175hp mercury black max motor. I have owned the boat for a few years now with very few problems. However this last trip to the lake, I encountered one, and it was from my own stupidity. While on a long run I was hearing a faint beep sound. At first I thought it was my depth finder, but eliminated that when I turned it off. Uh oh. The motor seemed to be running just fine. I didn't want to risk it so I had my brother in law tow me 4 miles to the nearest ramp. Upon further investigation, I noticed that my oil tank on the engine was only about two thirds full. Turns out I was just low on oil. So a couple of days later, I filled up my remote tank with oil, took it to my local lake, and while idling, popped the cap off on the engine tank. About 45 seconds later the tank filled up, put the cap and cowling back on, and ran around the lake for about 5 minutes, and all was well, no beeps. I load it back up, go to pull the drain plug and low and behold.... Oil is everywhere.popped the cowling off, and again oil all in the bottom cowling with a slow drip coming the open tube. So long story short, I believe the check valve may be bad now, the one that is supposed to prevent a vaccum from happening. Now here's where I need help. I have looked on several sites to order this part, mercury part number 42425. Its apparently NLA, No longer available, or obsolete. However there are mercury parts number 42425-2, and mercury part 42425-4 available. Will either of these two work? From what I gathered the 42425-2 is a 2 psi check valve and the 42425-4 is 4 psi? Is this correct? I believe what I need is the 2 psi. Thanks in advance for the help.