Mercury 500 thunderbolt 50hp lower unit chip/notch leaking gear oil.

[joeboater7]

I started noticing a few drips of oil under the lower unit in my garage and upon further inspection found a very small chip/notch on the leading edge of the lower unit that had a slight bit of oil in it. The chip was about an inch below the fin. I quickly checked the lower unit oil and it was indeed milky. I was about to jb weld the hole but put a toothpick into it to clean it, when I noticed there was a channel about the width of the toothpick in the hole at a 45 degree angle upward. That made me think the chip/notch/hole was supposed to be there, although old fuzzy pictures and my memory seem to indicate it wasn't there before. And the leading edge of the lower unit does appear to have other small nicks on it. There is no hairline crack around the chip/notch. Is this a water inlet? Speedometer? I have no speedometer on the boat. I would love to patch it and get back out fishing, but I, of course, don't want to make matters worse.

the motor is a Mercury 500 thunderbolt 50hp. Guessing around late 70's because that is the age of the boat. The serial on the motor is 4807141.

Sorry the pictures are fuzzy and out of focus. Let me know if you need something sharper.

Thanks very much in advance for taking the time to help me out!