Joe, Bill,

That's great input! Thanks very much! So the locking action is purely geometric/frictional? Because if there's nothing else going on in that bracket I'd conclude the lock where the lock rod passes through it must be bent or worn out too far. It does feel a little bit sloppy and as stated, doesn't lock at all.
I suppose I'll try to bend the lock a little bit and if that doesn't help I may have to weld the lock and drill a new hole with tighter clearance. Cleaning up the lock rod surely won't hurt either....

thanks! Matt