On Wednesday, May 22, 2013 3:49:32 PM UTC-4, wrote:
I have a friend who flew a DG-606 with internal gap seals. One day he went into a brutal, uncharacteristic spin that almost killed him. He got out of the spin at very low level. The glider was thoroughly checked to try to understand why it had reacted that way. It appeared that the internal aileron gap seals had failed. After replacement, the glider went back to its usual benign flight characteristics...

Now, everything will depend on the type of glider and the type of ailerons. Some older gliders had ailerons with a gap, by design.

Why would failure of a gap seal cause a spin?