Try a few drops of oil first, after that check your field strip screw. If that does nothing for you \/ \/
If it leaks down the barrel with the trigger at rest, you have a leaky powertube o-ring. If it leaks down the barrel with the trigger pulled, you have a leaky on/off (top) o-ring.
If that still doesnt fix you will need to mess with the lvl 10
I'm gonna do all these whippets and pass out, good luck OK.
-Bob Lee Swagger