Hi,
I have a sliding patio door, that requires a lot of force to toggle the lock - so far my troubleshooting has indicated a mismatch between the lock-side and strike-place/receiver side (sorry, I don't know what these are called, but have included the photos). Basically, exactly at the center of the lock (handle side), there is a metal projection (it doesn't project out) which when depressed, allows the lock lever to operate freely. When door is closed, I assume something on the other end pushes this projection and the lock can operate freely.
However, in my instance, if you look at the receiver, there is nothing that can physically depress the center projection on the lock/handle side, and hence it requires a lot of force to operate the lock (basically lock the door when closed).
Can you look at the images and let me know if you have a replacement part for the receiver? I don't know the make/model of the door, but have included the AAMA label. Hope it helps.
Thank you.
-Amarendra