There are only 2 areas Timmy's will really leak from
The first if the poppet, that's the valve which actually opens to fire the ball. if that's leaking you'll hear the air running down the barrel. If it's that then you need to replace the cup seal, you might be able to get away with removing it and re-grease but it's best to replace the cup seal.
Otherwise it's almost certainly going to be that a hose has come off a barb on the solenoid or Ram housing. Just take off the grip frame and make sure all the hoses are Ok and pushed well onto the barbs.
It *might* be a ram sleeve oring or solenoid but it's pretty doubtfull.
When you say leaking "inside", where abouts exactly?