Re: lower unit leak
How do you define "slight leak"? Was the oil milky? (water contamination) Dark but not milky? (not water, just not changed when it should have been) Pudding? (don't mess around, you have a serious leak) Metallic flakes? (probably some shifting wear/damage).
I'm not trying to be insulting, I'm just trying to see what your seeing.
As far as damage goes, if you have water in your gear oil, then you are ruining the viscosity of the oil. Contaminated gear oil is not lubricating your gears properly and will result in damage to expensive components.
Listen to robert graham and start with your least expensive parts first and check the gaskets/seals.