I have the SE. I had a belt shred after about 4 flights from new. Installed the MX400 grooved idler pulley, a little silicone, replaced the tail pulley and shaft and bent the boom slightly so the belt didn't pull to one side of the pulley. Many folks don't run an idler pulley at all. Bending the boom slightly if you have the aluminum will move the tracking on the pulleys (like the belt sander reference above). I wouldn't get too carried away with this but if the belt is always tracking hard to one side of the pulley a slight bend will cure this. I got a little carried away with this until I decided the main problem was a bad rear pulley (pressed on off center).

The old pulley was plastic and slightly off to the left. I replaced it with the metal Align one. If the gear is slightly off to one side the belt will hit the corner of the housing where it is cut out in front of the pulley (square opening in the housing). This only happens at RPM with centrifugal force arcing the belt into the housing. This cuts the belt.

WD40 is for metal and not very good at that. I use LPS 1 or 2 for metal on bigger things and gun oil with Teflon on models. Silicone is for rubber and plastics.