What does the forward flat head screw on the right front portion of the LU do? I'm not talking about the drain or fill/vent for gear oil. I'm talking about the one on the forward right portion of the bullet shape area forward of the prop. It has threads next to the head and a smooth long shaft at the end. I have removed it and put a new o-ring on it but that broke and some gear oil was leaking from it post lake trip. I ended up pulling it out and using a real gasket and now it's sealed. My question is what does that smooth shaft ride against from the screw? Also should that section have gear oil preset or does it mean a seal is bad between it and another wet zone inside the drive? Thanks for any info!