Last week I couldnít open the entrance door to our 1978 Argosy. The latch handle pulled open, but the slide bolt didnít move. When my husband removed the KT lock, he found that the tip of the lever that depresses the slide bolt spring had broken off. He removed the origninal thick rusty washer and put new thinner ss washers of the same diameter on either side of the shaft pin. Now the broken lever pushes on a washer rather than a pin. The cost was only a few cents and it works better than ever.
Another note: While you have the lock apart you may want to take the lever+shaft to a shop to have it spot-welded. The original job looked shabby.
How it looks now (with lithium grease):