1987 740 GLE ANTENNA

[BEMFICA1]

The antenna on my 87 740 just broke down. The interior plastic cord snapped. The motor still works,but I was able to get an entire unit at a local boneyard. Before I installed it I tested. The motor runs,but the mast
doesnt go all the way up (the last third). If pull it by hand will go up. Once
I turn the radio off the antenna goes all the way down.
The question is:
Is the mast still in good condition under the circunstances ?
If positive how can I overcome that situation? (make the last 3rd of the mast extend).
Tks for input.

[rlc]

Just carefully take it apart and clean it.