6' Marvin patio door. The locking lever under the pull handle
Thanks for writing in. Take a look at our 82-106 Thumb Lever. Keep in mind it may be worth checking to make sure your door's internal mortise lock isn't broken and the cause of the lever not working. To do this, remove your handle set from the door and attempt to manually 'flip' the mortise lock with a flathead screwdriver. if it fails to budge, then it is the cause of your problems and also needs to be replaced. I believe your mortise lock might be our 82-226, but be sure to go over all the pictures and dimensions if needed to confirm.
If the mortise lock hook flips up and down too easily, then the spring inside of it is probably shot. I recommend replacing it with a new one like the 82-226 I mentioned.