Re: Slight vibration
The shop would probably have just dropped the foot (bottom half) off the lower unit to replace the impellor. They wouldn't have pulled the lower unit off the transom so they could see the bearings and u-joints.
First sign of a leaking bellows is usually a growling bearing or u-joint. If the drive assembly hasn't been removed and inspected in a while, it would probably be a good idea to do so. It's pretty easy to do an Alpha (being an '82, yours is probably actually a pre-Alpha but there's no real difference). All it'll cost is an $8 gasket set. Put it in forward gear, 2 nuts to drop the trim cylinders, then 6 nuts on the back of the drive and it should come right off. It only weighs about 80 pounds, I can easily remove them by myself and I'm a scrawny little guy. It's nice to have someone to help you put it back on. If you've got water in the bellows, the gimbal and u-joints will be rusty and nasty. If you let it go too long, it'll rust the input shaft and take out the input seals, which will than allow enough of your outdrive oil to escape to ruin your upper bearings and gears (pretty much trashing the whole outdrive).
See, there's actually a reason Mercruiser recommends an annual inspection .....
