compression test, and couple other questions...

[Rollin Thunder]

Hi, I have somebody intrested in my boat and he would like a compression test done. I have a rebuilt by jasper 3.7 liter 4 cylinder mercruser engine. it was rebuilt in 06. What numbers should I be looking out for? also there was some oil leaking around the back of the valve cover. Its not much, but something he questioned, is that a gasket most likely, or am I looking at something serious? One other little thing is the alternator belt seems to like to pop off if we go over 3500 rpm, its not serious since you can just pop it back on, but something I'm confused as to how to fix, it seems to be at the right tension, and the bracket and all seem tight, any reason this would happen? Im worried as I need this boat to be sold yesterday, and dont want to scare a potentially serious buyer off. We took it out for a sea test Friday and spent about 2 hours on the water with him just driving around, and the boat ran very well, everything working as intended, Just some problems that seem more preventive than actually something wrong, But I have been very wrong before. Thanks for the help guys, I REALLY appreciate it.