try removing the accelerator control, remove the cover carefully and get some electric contact cleaner and clean it out.

Then when reassembling use some white lube and lubricate the plastic contact areas on the slide assy, then using silicone sealer reseal the box lid and around the wire harness where it goes into the box.

This box should be air tight so no dust can get in there and interfere with the LED emitters. These emitters if dirty will cause all sorts of travel problems if they get dirty.