I was just dealing with antenna problems the other day...though not what you are describing. It occurs to me that you might have an old piece of the flexible nylon geared line left inside the retraction reservoir and when your antenna tries to go down or up, it hangs up on the piece in the reservoir. If the motor "thinks" it hasn't reached the point for full extension or retraction, it will continue to push/pull against a heavy resistance...hence the heat. If you decide to check it out, removing the antenna motor and disassembling it aren't difficult. Just watch the little rubber bumpers that will come out when you disassemble. They tend to jump off their retainers on reassembly if you're not careful. The antenna motor housing can be unassembled by judicious use of a couple of small screw drivers.

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1987 300D with 201k miles.
1985 F350 Ford dually 6.9 diesel
1988 F250 Ford utiilty truck 7.3 diesel