Bob,

Friction has probably built up in your step rotator hub, to the point that
the step can no longer move forward against the air resistance.  

Similar thing happened on mine, and I was able to correct it by spraying
silicone lube on all bearing points on the hub including the plate against
which the coiled spring rubs.  I also relocated the spring attach point,
moving it further down the step to increase the moment arm.

Nowadays, I clean and lube the step at annual time, and that keeps it working
well.

Ken Lanham
'Windwalker'  N144L