From a machine tech's point of view.....if it ain't broke don't fix it. Best thing you can do is just clean string clamp and gripper surfaces, keep dust off the machine, and check calibration every once in a while (couple times a year or after 40-50 racquets). The "maintenance" issues I get calls about are from the curious folks that just can't help themselves and they take things apart to try and lubricate moving parts, clean inside the tensioners, or just want to better understand how something works. That usually results in linear grippers coming to me in parts in zip lock bags, tensioner displaying error codes, followed by the "I'm not sure what's wrong, it was working fine a little while ago?" Lol
My first machine was a dropweight. I don't even remember if I cleaned the clamps. The only maintenance issue was a broken spring in the clutch assembly.
With lockout machines came fixed clamps and the need to lubricate the glide bar rails with grease and clean the clamps with alcohol. My first lockout machine was a True Tension machine that I purchased used. When I disassembled the clamps the first time to lubricate them I discovered that all the dowel pins in the clamps were broken. That's the only thing I remember repairing on that machine. It was built like a tank.
I have worked on a number of Ektelon H machines. They are mostly trouble free. You still need to lubricate the glide bar rails and keep the clamps clean but I don't recall ever having to do any actual repairs. For a time I worked for a sporting goods chain and their tech came by one day when I was out and drenched the machine with WD40. He managed to soak the brake pads in the tension head. I had to unsoak them with alcohol to get the machine to work again.
These days I string on an eCP machine. I have strungs thousands of racquets on it. It is a work horse but from time to time there are issues. I wore the brushes in the motor down to nothing recently. I am still working on that repair because the bearings in the motor are in need of replacement and have not arrived. I am also waiting for delivery (sometime in May probably) for a failing potentiometer that is causing the unit to stop pulling every couple minutes.
The motor in turn drives a lead screw that is supported on each end by a mounted flange bearing (mfb). I have replaced those 4 times, a job that requires quite a bit of disassembly. An mfb is an interesting beast. It is like your eyeball and eye socket sold as a unit. Your eye can look up, down, left and right. An mfb is similar except imagine if your pupils could rotate at some serious rpms. When an mfb goes bad though, instead of the pupils spinning, the eyeball starts spinning in the socket and the pupil stands still. Time to replace.
On the eCP I occasionally have to remove the clamp bases from their tracks and clean, clean, clean and then lubricate the track and the "T" that anchors the base to the track. I have disassembled the clamp bases themselves a couple times. The first time I think I was just trying to figure out what was leaking out of them and messing up the tracks. Bearing grease.
I clean the clamp teeth every morning with a pipe cleaner and alcohol.
Although there are more issues with the eCP, the pros far outweigh the cons and I am doing everything I can to keep mine going.