Rear window leaking

[Mx450ltr]

Hey guys I have a 96 reglular cab with sliding rear window I have had carpet out 3 times now rear window keeps leaking and i tried to fix with silicone doing it around window and body but it will leak and go down side and I have a pond Inside my truck. Anyone have any ideas on how I can fix this myself or should I take it to have a rear window tooken out and put back on with new seal?