do these units have a separate steering pump?
reason i ask is some newer machines utilize the hydraulic pump/system to run steering now. The hydraulic pump will jog at a slow pace and divert fluid to the steering through the steering proportional valve. That would explain why the steeering column is getting hot. If your having overheating issues the dash should set off an alert/fault notifying you/them of it. If it's not triggering an overtemp fault then the machine is running in allowable parameters. I wonder if the tech's have tested the temp and pressure sensors or checked the pressures and/or settings in the system that control the pump 'on/off' time.
I saw this "new way" of powering the steering in some of the earlier hyster trucks back when the AC powered motors, controls started becoming a thing.
These new systems trigger the power steering multiple ways, interaction with the foot pedal when in gear, movement of the steering wheel via a haleffect pot in the steering column combined with a pressure sensor inline with the steering pressure line. (older systems used the pressure sensor at the steering pump).
If this unit does not have the integrated steering in the hydraulic circuit and does have it's own motor then i would be looking for some other electrical issue causing it to trigger the hyd pump when it's not supposed to, a hung switch or bad sensor/switch in the controls.
As far as the dealer tech's? and knowing how to troubleshoot them? First off they shouldn't be sending out a tech that is not trained on the model lift you have. If they are not certified on that model the engineering at Yale will not deal with them.
All dealer tech's have a hotline to the mfg so if they have problems diagnosing any issues they should be contacting engineering at Yale for help.
Communication between you and your tech is imperative and if he's not doing that well enough for you then request another tech till they send someone that knows what they are doing. A good tech will tell you everything that is going on, work with the mfg, and won't leave you hanging and will always follow up and resolve the issue in a timely manner. (please do complain to the dealer about the poor service and that should get them off their butts, if it doesn't then find another dealer).