Got an STI para in 40 S&W from a friend to look over (typically when the gun is due for a full strip cleaning). He pointed out that after initially running the slide, the grip safety sticks out. There is a definitive click when the safety pops in. Other than that, the weapon functions fine; thumb safety, trigger, hammer fall, all function as they should. Everything is clean and polished. I'm thinking the leaf spring maybe the culprit.

Anyone else encounter these issues? Thanks in advance for any insistance.

Maybe the hammer strut is interfering with the GS. Definitely check the sear spring as you mentioned too.

So after looking at all the inner workings and manipulating every  way but loose, I determined that the grip safety was the issue. Despite no apparent burs or rough spots on the safety or on the frame, the bottom of the grip safety was hanging up down by the mainspring housing.  

Try as I may to get the existing parts to work, I had to put in a new grip safety.