Why has the range of movement of the control surfaces changed over the past year? During the annual inspection on our glider, we discovered that the maximum downwards extension of the right aileron (i.e. full left stick) was outside the manufacturer's tolerance. The measured value was 32mm and the manufacturer allows 40mm &plusmn; 5mm.

What are the possible causes of a change in the geometry of the system such that the ailerons no longer move in the range they did last year?

For reference, the glider is a 1983 Schleicher ASW19b, with standard l'hotelier control connections and aluminium push rods over bell cranks in the fuselage and wings.
We found the problem. The control stops are under the seat and are made of plywood. It looks like at some point in the past someone had added a small layer of plywood to reduce the control deflections but that over time the glue had deteriorated or the wood had swollen, so that there was now too much stop. Removing the extra ply and sanding the glue back to the wood fixed the problem.