Mega Man,
   Jag antennas are rather expensive -- in comparison -- so you may want to
consider a re-build.  The antenna shaft its self is connected to a stiff
nylon "string" much like you would have on a weed whacker -- but much
thicker. This nylon coil is toothed so that it runs through a gear up and
down to make the antenna telescope. The gear is run by the motor in the
antenna housing.

There is a disc that has a metal contact on it that turns slowly when the
antenna is moving. When it reaches either end of the span, it shuts the
motor off. If the antenna reaches either end of its expansion or contraction
prior to the motor being shut off, there is a built in "ratchet" effect that
takes place so there is no damage done until the contacts hit and the motor
shuts off.

What is taking place on your system is that the "disk" needs to be
calibrated to the throw of the telescoping antenna. In better words, it
needs an adjustment so it shuts off as soon as it reaches either stroke
without much ratcheting action.  In order to do this the entire assembly
needs to be taken apart and adjusted.

If you are mechanically brazen and not afraid to go where few have tread
before (or if you have a spare at  the ready to purchase if you mess this
one up)  Then go for it.  It really isn't all that complicated if you keep
it all straight when you take it apart.

An aside -- I saw a car with a NONI Juice sign in it tonight in a parking
lot!!  How strange

Cheers
webserve