Now it's time to put the rheostat back together. Put a little bit of di-electric grease on one end of each spring and place them back in their holes. The grease will keep them in place as you reassemble.
From there you just need to hold the slider onto the spring and place it back into the housing. The metal clip is what holds the dial/spring/slider assembly onto the coil housing, so you will need to hold it in place as you slide the metal clip back on.
Once it is back together, you should try rotating the dial a few times to see if the slider runs good along the coil. When I tried it I found that the slider was now pushing the coil out of its track - see below (it shouldn't be sticking out like that).
So, how do you fix that? More di-electric grease, of course. I lifted up the coil, placed a few globs of grease in the track and then pressed the coil into the grease. Worked like a charm, the grease held the coil in the track and the slider moved smoothly across the surface of the coil. Note that you can rub a little dielectic grease on some of the metal components to keep them from corroding, but avoid getting it on the contact surfaces.
That's it! As they say, assembly is the reverse, right? Mount the rheostat back on the panel and reconnect the panel.