old snapper

Just bought an old working Snapper, and Im putting some time in it to make it better. I'm having problems operating or trying to lower and raise the mower
deck. The lever that goes thru the different levels seems to be frozen.
Any ideas as to how to get unstuck.
Have no idea what the model is.There are no placards. All I know is that it has 12.5hp and a 28" deck.

Thanks in advanse!!