Sliding door lock won't lock

My 20 year old patio door lock has stopped being able to lock the door. The lever will not activate the hook to catch on to the strike plate. The only markings on the existing lock are what looks like a an SC as you can see in the accompanying photo. It appears that your part 82 Dash 218 is identical to my lock. Please advise so I can purchase accordingly. My luck is 3 11/16 from the center of the two installing screw holes.