After reading around I decided that replacing the mast on my1994 ls400 power radio antenna would have it back to working order. After removing the old mast, inspecting the motor housing to check for broken teeth I put it back together. Upon feeding the new mast into the tube I heard a lot of grinding, then the gears would catch, pull the mast in for a short period, then stop.
After trying to feed the mast in numerous times I gave up. I assumed that all was lost. The sound of grinding gears lead me to believe that they had been ground out due to the old mast being stuck in one place. After searching around I didn't want to pay $100 buck for a used unit. After a trip to the local breakers yard there were no ls400 there but a few es300's. The motor looked to same and so I got it for only $20, thinking I could change out the motor housing only.
Took them apart to find out the the inner workings were the same. Upon inspecting the gears I found that the gear coming of the motor worm drive was flatted with no teeth left. I scavenged the gear from the es300 motor housing, reassembled, the new mast fed in like a charm!
So even if you have tried a new mast and it doesn't work but you can hear the motor turning, Check the gears and scavenge from any similar lexus power antenna! Fixed mine for a grand total of $20.
Pictures below, hope this helps someone else out.