Leopards are ambush hunters. They might kill a baby gorilla or a female gorilla, but they are not trying to square up with a "healthy male silverback" gorilla. For basic reference a silverback is about 450 pounds and about 10 times stronger than an average adult male. Silverbacks can literally crush skullsNaw leopards actively hunt gorillas.
Gorillas have skin similar to humans in that wounds split open, instead of self closing to reduce blood loss.
Higher primates are easy work for predators...