passenger door lock issue

Hello everyone, I am experiencing troubles with my passenger door lock. My drivers side door will manually lock with the key however will no remain locked. I believe this is due to the passenger side door. Now when I use the key on the passenger door the key will not lock the door. Seems like the lock is stuck? Anyone experience such issue, also what part of the door lock would need to be replaced? I see a variety of door lock parts on ebay.

 

Thanks! I will definitely give it a try, if its easy fix that would be great. But I feel there's something that needs replacing otherwise the previous owner would have straighten it out prior to my purchase.

 

That makes sense and sounds spot on! Thank you gentlemen for your responses!