Re:
It is a possibility that the lock out is jammed in locked out position if it has been forced beyond it's locked/unlocked positions the shaft can break. But it's more than likely that water has gotten into needle bearings and the races they run between.
The needle bearings/races need regular checking and greasing to keep them working OK, if there's any rust at all, the tolerances will be zilch and they'll jam.
A Lefty with rusty bearings/races can be rebuilt like new with new bearings/races by those who have access to the tools and spares needed. There are several different tools just to remove the damper cartridge alone, each different Lefty/Headshok seemed to require it's own specific "Castle" tool. Bodging a tool to remove cartridge after undoing the top cap will probably result in the damper shaft being scored and that's it effed.
So rusty bearings races relatively cheap to rebuild, a jammed/fecked cartridge to replace isn't cheap. If you have a Google you'll find several Lefty/Headshok rebuild specialists in UK who will take yer money to make it like new.