The mechanism that opens the latch on our front door has broken. This is not as serious as it sounds because the main lock is a deadbolt (which is working fine). After some disassembly (OK, a lot of disassembly) my best guess is that there is a spring broken in the main latching mechanism. Photo is below, but the brass plate does not appear to be easily removable. It's connected by what appear to be crimped metal tabs from the rest of the unit. I need that unit.
The operational problem is that the peg the handle is supposed to push up to rotate the spindle is locked in the "open" position (completely clear of the slot where the thumb piece fits).
I am not a locksmith. I will be very grateful for any suggestions. And I'll apologize in advance for any vagueness or bad terminology. I'm fairly good with tools, but don't know much about locks.