How to Seal leaks on an air compressor system
Rubber (better, usually) or plastic tubing on a barbed joint is not a suitable place for any sort of sealant, and none should be required.

If the tubing is cracked, either cut off enough tubing to remove the cracked end (if it's just at the end) or replace it. 

Otherwise, push the tubing fully onto the barbed fitting and tighten the clamp(s) - in some cases adding a second hose clamp with the clamping mechanism rotated from the first hose clamp (so if one has the clamp screw at 3 o'clock the other would have it at 9 o'clock) may help - often the barbed fitting is long, and clamp used is short. 

Oversized clamps wound down too small may have excessive not-roundness near the clamping mechanism; a properly sized one will work better in that case.