As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB-OUT, THE FIRST OFFICER'S R2 SLIDING WINDOW DEVELOPED AN AIR LEAK. RETURNED AIRCRAFT TO MKE. FOUND OBSTRUCTION IN THE R2 WINDOW TRACK. REMOVED OBSTRUCTION THAT WAS SEATED IN WINDOW TRACK. PRESSURIZED AIRCRAFT AND OPERATIONALLY CHECKS GOOD IAW MM 560000.