I have never worked on a yammie, but some seals you can do...some seals you have to have the tools to do it with or risk messing something up.
Before I did anything I would drain the fluid and see if it has any water intrusion. Oil leaking from back there can come from the powerhead...as the exhaust runs through there...in winter we lower the engine down and sometimes oil or fuel oil can leach its way down through the exhaust picking up gunk on its way and when it exits it looks like LU lube.
If your lube is pastey white...you have a problem. If you drain it and its clean...replace to the little orings under the drain and vent screws and don't worry about it. If it is lube, and its dripping, you have a good leak..normally we do not see lube dripping like that...normally you'll just find white pastey looking lube. The viscocity of water is way less than oil and the LU can actually hold a vaccuum while you are running due to everything moving inside. Much easier for water to get in than oil get out.
Check the fluid...if white, take the lower unit off and have it psi tested and vaccuum tested. Shops should do this cheap if you take the unit to them. If you can, go with them and see where the bubbles come out. If its a seal that you can replace, replace it. If not let them just put new seals in it.
Something else you can do...go to the parts department at your shop and have them print you out an exploded diagram of your LU. They have all this on computer. Look it over. You might see that you can do it yourself.
If you decide to take it in...take the lower off and take it in. That will save you probably an hour labor charge. I would do water pump impellor too while I was in there. Just some thoughts. I'm a penny pincher...lol :D
"But if serving the Lord seems undesirable to you, then choose for yourselves this day whom you will serve, whether the gods your ancestors served beyond the Euphrates, or the gods of the Amorites, in whose land you are living. But as for me and my household, we will serve the Lord.” Joshua 25:15