Kick down servo pin?

Had a leaky trans pan. Took it to my mechanic, who said he couldn't seal the pan because of the gasket surface was not flat anymore and he couldn't get it flat enough , to seal all the way. So I ordered a new pan. He also mentioned that the kick down servo pin was leaking and could fix it when he puts the new pan on.

Exactly where is this pin and how could he tell it was leaking. Also, what does it do?
Thanks