Anyone have a NordicTrack skier?

I ran across a NordicTrack ski machine in pretty good condition at the thrift store for $15.



I have a question about the glide buttons on this - they are designed to wear down and provide lubrication. Is it required to replace them periodically? I have read that the sides of the skis can be lubricated with paraffin wax. Would this be sufficient instead?



Any tips on usage or maintenance?



Thanks.