It seems I've been doing a bunch of drive shaft seals lately too. I just resealed a drive for one of my customers yesterday. The guy's boat is a late 80's 19 foot cuddy runabout with a 3.0 liter Mercruiser, hadn't been maintained for some time. I ended up doing almost an overhaul on the drive system - rebuild carb, fuel pump, shift cable, gimbal bearing, drive shaft bellows, alternator belt, a bunch of rewiring, it was a mess. Well the drive bellows had holes in it and the upper shaft yoke seal was leaking bady, there was oil in the bellows and water in the drive oil. I replaced the seal and pressure checked the drive, the other seals seemed to be ok. The shift cable was rotted thru at the bell housing so when I was removing it it fell apart.