Door lock help, Doesn't work 100% Options

[screenguy914]

Need assistance with my passenger door before I tear into the door.

Able to lock/unlock from the inside and outside with the key
Interior and exterior door release handles operate

However, when locking with the key, it rotates only about 10 degrees, then stops. I should be satisfied, but I fear it might get worse.

Is this an issue with the key tumbler or with the exterior door handle mechanism?

Thanks

[Mark Henry]

Just did this on the passenger side for a broken cam, a bit of a PITA if you have big mitts, but a fairly straight forward job.
I just did my passenger side, now it's obvious the left side needs doing as well. I found a better handle but I had to drill out the rivet and tap for an M6 bolt and swap the lockset. This handle already had a good original cam so I left it in and cleaned and lubed the rest. If you pull the lockset just take care that you don't let the wafers fall out. The lock mechanism does come out without removing other stuff, I had to turn it 180 around the window track, but it did sneak out. The old grease had mixed with dirt that turned it into cement.
Now it works and locks excellent and I don't have to worry about locking myself out.