After playing around with it some more, I fear you are correct. I
didn't explore this possibility but it would appear the shaft inside
the cable is what is causing the resistance. Is there any way of
servicing or lubricating it?

The grease fittings are to grease the tilt pivit, not the steering
cabl;e. Dies the shaft that you cionnect the steering link to move in
and out of the tube easily? You should be able to pull it out with the
collar nut off. It soulds like you are just moving the cable, not the
shaft. With the collar nut loose does the wheel move OK? just the
whole cable sheath moving back and forth from where the collar nut
threads to the motor?
If so that is good news. It means the cable is OK. The shaft is just
stuck in the tube.