Was having trouble with the power antenna. Bought the new mast, took the broken piece out of the drive, the new one refused to engage. Oddly, the nylon gear strand on the new mast curls opposite the proper direction (teeth toward the outside of the arc) so I took the whole thing out, fed it in manually with the drive cover off until I was sure it would spool correctly, put it back together and put it back in the car. Of course the first thing it did was spit the gear strand back out again. Twisting the mast helped not at all. With my lovely assistant turning the radio off and on again many times, I finally gave it up and disconnected the motor. My guess is the drive gears must just be worn enough to slip past the strand teeth, though they didn't look it. Is there a magic trick to this? Is that drive gear available on its own or do I need to find a whole new drive unit?

The curl is toward the teeth when it is shipped, normal. If the mast is not bolted to the fender when you turn to power on, the whole mast will lift right off and you will need to feed the plastic in again.
When feeding in the plastic it will stop, and then you need to "force" it in another inch before turning turning the radio off. Just make sure you put the collar on the mast and tighten down the large bolt.

Klaus
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Volvoless. Sold the R. There is now a void...

Right, I'll try again tomorrow. What I meant is that on the old mast, the teeth face toward the inside of the curve, and the other way round on the new one. Figured it just needed to be spooled correctly a few times to give it the proper attitude. I'll try with the mast bolted down this time, Thanks.

I couldn't remember the details (that's amazing Klaus), but I do remember this thing is stubborn. And I do remember the curvature was exactly opposite what you want it to be. I wasn't confident I could get it to engage without ripping it apart, as it sounds you did. In the end I seem to recall the trick is Klaus' technique. I believe I also powered it up without some hardware, and it pushed itelf apart as stated. Perseverence comes in handy with this thing. I did mine alone - having an assistant sounds sublime. Good luck.