The locking issue in your 65" Slo Rise roller shade is most likely due to a worn or faulty internal spring mechanism. Since your shade retracts properly but fails to lock in place, replacing the spring will restore the locking function. For a 65" wide shade, typically mounted on a 1.25" diameter tube common in RVs, you should use the "Large" size 1.25" replacement spring designed for Slo Rise shades. The spring mechanism is usually located on the side with the flat metal tab or adjustment knob. If uncertain which side to replace, installing the spring on either side will address the problem as the spring controls the tension and locking. You can find the correct replacement spring on Elkhart RV Parts' website under the Irvine Replacement Spring for Premium RV Roller Shades, Slow Rise version. If you need help confirming tube diameter or side, additional measuring instructions and support are available on the product page.