I always used plain old candlewax. Just take a candle stub and rub it hard into the teeth. Liquids and sticky stuff like vasaline attract and hold grit, #1 enemy of soft cast zinc sliders.

If you ever need to replace the sliders on your soft top pick up some stainless steel ones from a marine upholtery supply shop, they'll never corrode again!

Take an old slider in with you if you go out shopping for new ones. The #8 and #9 coil sliders look almost identical and will not work if swapped.