how do i replace rear left seat belt in 2010 crew cab

My 2010 left rear buckle had a problem. Bought a replacement seatbelt system for $108. Directions require removing rear seats. Not easy but with patience removed seats.After removing the retractor system I began to thread the belt out of the guide bracket at the top of the seat. This small "soccer goal post" looking metal guide would not allow the buckle to pass through. The rear glass does not allow for enough clearance. Two "pros" suggested having the rear window removed. That requires buying a whole new window most of the time since the unit is glued in and will often break. Glass shops would not perform service to just remove and re install the same window. Wanted me to purchase a whole new window.