I have this old lock - you use key to turn the core and then push the lever to activate the latch.
First the lever was sluggish and stuck, a little bit of WD-40 did loose it. But this time it won't work.
It reads Kwikset, anyone know the model number and how to fix or replace the mechanism?
Thanks.

 

Here is the photo of the lock.

 

I don't have much to contribute here, but since nobody else has responded, I'll submit that having done residential locksmithing from 1975 to around 2000, I've never run on to this model, and Kwikset has been the most popular house lock brand for decades. I'm pretty sure this has been discontinued for years, in favor of the combination Passage Handleset and design-matched Deadbolt installed above. And unless the latch shown in your photo is broken/faulty/stuck, it appears to not even be a "Deadlatch", meaning, very low security. If you happen to have a deadbolt on this door, apart from the this lock, simply replace this with a passage set, (either a grip handle [Handleset] type, or Cylindrical type, [plug the lower hole]), because using the Deadbolt offers 10X the security of a spring latch, (what you have).


Grip handles with thumb-press (AKA "Handlesets"), are more expensive and fail at higher rates than ordinary knob or lever locks, due to the unavoidable mechanical translation from up/down thumb-press movement to lateral latch movement, and most designs depend on the linkages being well-greased to avoid early failure, and even then, sometimes they'll stick or operate sluggishly.


If you don't have a Deadbolt above, but want good security at low cost, replace this handleset with an inexpensive Passage knob or lever, and install a moderately priced Deadbolt above.

 

If the problem is the latchbolt, they are readily available. If the interior sets are Kwikset, you can "borrow" a latchbolt from an interior door and get a replacement later.

If its not the latchbolt, and you can't fix the problem, I'm afraid your only hope would be New Old Stock.

 

Kwikset is a low end brand and I've never known them to be serviceable. Personally, I would be looking for a better quality replacement instead of trying to fix this.

 

Thank you all for your expert info.
The best solution is replace it with a high security new lock.