of the track to expand it a little bit. Also used some freezing spray (air duster can upside down) on the white swivel slider. Combination allowed enough give to get the track end inserted over the nylon swivel (yeah!!!)
Figured I'd post in case someone else runs into the same issue. They track end on both my new slider and the old one was tighter at the bottom than the top -- swivel slider runs up/down just fine once I got it inserted (ie., no binding)..