I do the impeller about once every two years - humorously, that's been because I've had something else fail each year that takes me into that portion of the drive for some reason or another. Otherwise, I'd let it go out to 3 and see what shape the impeller is in. Each time I pull 'em, they look nearly new (which doesn't always mean much).
Unlike Bruce, I am a mediocre mechanic on my best days ... I've never worried about lining up the ball gears. I've been told it really doesn't matter, and so far hasn't seemed to.
The Stringer is a funny critter. It's a pretty robust system on the overall, and when you figure that my unit is 40 years old and still runnin' that shows some moxie. They can be finicky though, and they know when you're not looking. You have to stay on top of 'em, and that means you're constantly needing to do maintenance, check for water invasion, etc., etc. They're probably a little over engineered in some regards, and that has an effect too. It'll make a mechanic outta' ya'.
On the plus side though: I like the fact that the power is delivered to the stringers as opposed to the transom. At least in terms of hull noise and vibration, my boat is SIGNIFICANTLY more quiet than the newer I/Os I've been on of a similar size. At low speeds (especially no wake) I also believe I've got tighter steering and better control than the newer I/Os.
The electric shift has a bad reputation, but to be honest - I've never owned anything but electric shift outboards and (now) a stern drive. And that is the only part that has never given me an ounce of trouble on any of the units. All my problems have been in the upper gear case or short in a wire harness. I think the ES shifts more smoothly in and out of gear, and I think you get a more instant power application (very helpful when maneuvering at slow speeds). So, to be honest I really like it.
Would I tell ya' to go out and intentionally look for a 40 year old electric shift? Probably not. Would I suggest you buy one when there's a comparable boat with a Merc sittin' available? Probably not. But, I'm not afraid of the drives and if you have one you can keep 'em runnin' very nicely.
