How do I access the seat belt retractor hidden in the rear seat back to release the tension on the belt. It will not extend.

 

i had this exact same problem with the center belt when i first picked up the car. Dealer had to replace the entire seatbelt

 

Likewise - had to take it into the dealer. They fixed it and then moved the location of the plastic stop on the belt so the belt wouldn't retract as much.

 

I had same issue which is related to the folding rear seat on the GLK as mentioned in the owners manual, but I found an easy, no-cost solution. If the dealer tells you the complete assembly needs to be replaced they are misinformed. Lift the rear seat bottom cushion to access the center seat belt anchor bolt and remove it to free the tension on the strap. With the seat back in the upright locked position, pry off the plastic trim piece where the belt goes into the retractor mechanism and just work the strap up and down till the tensioner releases on its own. Then I sewed a small black button 3 inches further inward from the existing button to keep the belt from retracting too far into the retractor mechanism, Reinstall the anchor bolt and lower the seat, should work fine.