If a light cleaning and spray with some SailKote doesn't help the mast car to slide, you can try doing a really good cleaning of the track.
These are the steps we perform for a very
thorough cleaning: It takes just a few minutes. It can even be done with the rig on the boat. We usually do this once a season, and more often if we've been in a very sandy windblown environment.
You will need a #2 Phillips and a flat head screwdriver, some mild solvent or window cleaner, a small tooth brush (an old one that you don't mind trashing), or a couple Q-tips, a rag, and some SailKote.
1) Place the folded rig on a clean flat surface, or, leave it on the boat.
2) Remove the small retention screw and pull the main masthead (the one with the shrouds and halyard pulley) off of the main mast.
3) Unhook the bungee from the front of the car.
4) Unscrew the bolt at the rear of the mast track.
5) Slide the mast car off the back of the track.
6) Use a solvent and an old tooth brush to clean grit and lube buildup out of the track.
7) Lightly scrape the bottom of the mast car with a flat metal surface to clean off any sand or grit particles that may have imbedded themselves into the plastic.
Wipe down the mast car base and track.
9) Spray SailKote inside the track and on the bottom of the car.
10) Let dry and reassemble.
11) Make sure that the halyard and shrouds are clear and untangled.
12) Test by raising and lowering the rig.
This should do it. I hope it helps!
Tight rig tension can also cause mast car sliding issues.
If after the cleaning the car, it still sticks, let me know. I can guide you through easing up on the forestay and re-setting the tension. It's pretty easy.