The key to a long term solution is to get the old, polluted, sticky grease off the rail before re-greasing it. I like using moly grease (molybdenum disulfide) for automotive applications due to the wide temperature range it remains stable. I agree, if you’re just going to spritz something under there, go thin. Otherwise, unbolt it, flip it over and spray some solvent on the tracks to get the old dirty stuff out. Then re-grease it and it’ll last the rest of its life (another 20 years 