1986 4000S, Motorized radio antenna

[Peter Biernacki <pbiernac@ea.oac.uci.edu>]

The car in question is a manual 1986 4000S with a 1.8L 4 cylinder
engine (7/85 production date).

The antenna motor is finished.  The housing has cracked and it's a mess.
I disconnected it from the power source and manually extended it so that
it at least works.  Though the gain feature no longer works obviously.
Does anyone know of a replacement motorized antenna that fits and works
well and DOESN'T cost an arm and leg, like the Bosch factory antenna?

Thanks,

Peter