Yeah, it will require you to pull the door skin off to peek at what's up. Tom has become very proficient at this in his Audi.

Being a PA bread and born man, he is disliking our California heat, Suki. I give him props for learning when to get the work done, this AM he was able to replace a coolant sensor and the front control arms in about an hour and a half before the garage started becoming an oven X10:00 am.
I looked around the 4runner forums for ya and didn't find anything that screamed at me except normal wear and tear. Whatever the plastic part you heard could be getting in the way of the mechanical handle function. Maybe you will get lucky and it will end out being a retaining clip that has popped off.
Let us know what you find. We're happy to help.