I'd say of the ones I saw, you had these constructed of cheap (potmetal-like) stuff that wasn't designed for lengthy use or somebody thought it would be ok. Which surprised me...sort of like using rubber tubing for brake lines or something. The sort of thing somebody with any wits at all wouldn't consider. The motor only failed if something in the transmission side failed, seized up completely and caused a fatal overheating of the motor. Which I never experienced, but friends told me they did. Remember, on the MG it was Lucas Electric branded stuff. The Datsun stuff...I was never really certain who over there made it. It seemed to me one copied the other. But it didn't matter. The shaft was the number 1 culprit, the gears were number 2 (but some people opined the gears were destroyed when the shafts went wonky and it was going to be hard to disprove that) and it was usually due to accelerated wear or accelerated wear that simultaneously caused things to no longer mesh properly. The ones I took apart were packed with grease, but if you have cheap metal (think the kind of stuff a keyed ignition module was made of), it doesn't matter. When the stuff crumbled, cracked or started coming apart the fat lady had already been singing long enough to be hoarse and tired. Remember these don't spin quickly but they have a decent amount of torque (which as we know at higher rpms will often be lost). I've seen the same sort of planned obsolescence in the Ford/Mercury/Mazda airconditioning air blend controllers. They're designed with only an elementary knowledge of things mechanical and they last about 1 year each. A single 10 cent metal collar would make them last nearly indefinitely. I don't know of any US made vehicles that used the cable wiper scheme, but many US made vehicles used (and still use) the same scheme for electric windows. In those, the driven parts are made of nylon, delrin or some hybrid industrial plastic. When it fails the window just drops to the bottom of the track and you have to replace the entire she-bang because of one failed plastic part. The cable drive part will usually be okay, but the plastic teeth shear off leaving nothing for the screw drive to engage.
