I assume the "slide release" you describe is actually the part properly known as the " slide stop" and it "fell out of the frame?" Will it hold the slide locked back? Will the slide lock back when the last round is fired from the mag? With the slide stop properly and fully installed - does the rounded end of the shaft protrude about 3/16" beyond the right side of the frame - if it doesn't - the shaft of the slide stop is broken.
Also check to assure the "plunger tube assembly" is complete in the plunger tube. If it isn't, that would enable the slide stop to fall out AND not hold the thumb safety secure in either the "safety on" or "safety off" positions.
It's not likely something is "worn" as much as either the slide stop is broken OR in the process of cleaning the gun, the plunger tube assembly fell out of the plunger tube and was not replaced in the re-assembly of the cleaned gun.