The safety of the Walther PP is similar to the safety of the Mauser HSc and the Walther P38. The safety lever is attached to a drum. One side of the drum is solid, the other side is cut through. In the safe position the solid face of the drum prevents the firing pin from moving forward; the cut through position allows it to pass through. The safety is retained by a pin on the toggle side of the drum. Once you have the slide off, take a look at the drum and start by lubricating it.
First picture is fire, second is safe.
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