I would do what Javelin said. Either put a bead of silone or the correct caulk over the top of the window frame or remove entire window and start from scratch.
All else fails look on line for leak detetion:
A few month ago MH magazine did a write up on leak detection. There is a company(S) the goes to the Dealerships and I think your home, they took up a pump with some smoke (no odor) and pressurize the RV and then all the of joints, window seals, door seals, vents, holes will leak smoke then they mark the spots for you to be repaired by your dealer (or yourself if you can).
Not sure how much that would cost but it could be an option if all else fails to seal the window.
2017 Axis / 25.4: Big Foot Levelers, Aims 1200 Watt inverter, Ceramic Window Tint, Full River AGM 6V batteries, Front Hellwig Sway bar / Rear Track Arm, Safe T Plus Steering Stabilizer, PD 4655 converter, Hard Wired Surge Guard, WEboost + WiFi Ranger, LED Headlights/Driving lights, Fresh water surge tank, Black Tank Tornado flush, 4999 zip ties.