Motor pics

[DonDon]

My niece and her hubby were over to the house last night so I only had time to take the cowling off and take a peek at it all. First tie I'd seen her in 2 years so it was a fun time. Here's a couple pics of the motor. a couple trips ago I filled the oil reserve tank op and when I trimmed it up, I noticed abit of oil on the deck of the boat. I assumed I over filled it and it was just leaking on the deck. Top pic shows abit of oil still under the motor. 2nd pic is the oil tank. Someone said something about a vacuum and there's a vent hole on one side of the top. Is there a cap missing or is that there to let air in so the oil goes down easier? 4th pic is just of the side of the motor.
BTW, I turned the key ON last night and it was still doing the BEEEEPPPPPPp so that tells me it's a sensor.