Once you get it clean as above, go to a hardware store and get a tube of silicone grease, and apply a tiny amount where the track slides, roll the focus track back and forth several times, then wipe off excess with a q tip... Just leave enough on that you can barely feel the grease film...

If it is still binding, there still might be dried grease, or a little fuzz ball that worked it's way onto the slide... Repeat above steps...

If still sticky and you get track apart, rub slides with toothpaste, as this is very slightly abrasive, and the fluoride will prevent oxidation, then clean very well and repeat above steps...

Steve K