My power antenna failed on me in the up position. This is caused by the nylon cable breaking inside the motor housing. I had to remove the 10mm screw that holds the lower motor housing to the car and then loosened the silver mast-to-motor bracket and then loosened the set screw holding the mast tube in place. I pulled the mast tube out of the housing with the mast and cable coming with. Only then did I have enough room to get the antenna out. So I purchased a replacement mast on eBay before I found out GM's part # 10256439 is the GM replacement. Part # 10402860 is the entire motor and mast assembly. The mast is removed by loosening a screw in the middle of that metal silver bracket that attaches it to the motor head and a set screw on the opposite side that we're working on. Loosen the two small gold-colored screws holding the motor down (or remove them) and pull the motor up to disengage the gears (or pull it out and let it hang by the wires). Pull the mast and nylon cable out. Since the cable was broken and a piece still inside the winding, I had to take the motor assembly apart. One side has 4 'rivets,' this is the side we need to work with. Drill just the head of those rivets CAREFULY! I wasn't so careful and I'll show you what happened later. You could use a Dremel to grind them off too and that's what I SHOULD have done.
I took out and cleaned the black dirty grease off each piece (which I will not show since it's the opposite of assembly which I AM showing). It was so gummed up and dirty that I couldn't take good pics to show WTF I was doing. So I photographed the re-assembly process. There are some really small washers so read this all the way thru so you can expect them and not lose em.
From fully disassembled the only piece remaining is this white gear off center. Clean it best you can and clean out the inside of the housing. I smeared everything with synthetic grease (red goo) as I put it back together.
Re-install that gear with the nipple flat side up.
Re-install the LARGE gear. I greased the teeth. I didn't pull all the white grease out of the grooves in the top, there just wasn't a point to doing that. The two towers should face up.
Grease and install the roller shown upper left.
Cont'd next page.