Is my old freezer safe?

We have just bought a new freezer and have promised our son that he can have told one as he desperately needs one, and cannot afford a new one. We have pulled it out and switched it off to defrost it ready to take, and noticed that the back is damp (more or less at the cable entry point), which seems to have been 'packed' with some sort of silicone or gel. Getting close to it you can notice a distinctive whiff from the same area. I'm not sure whether the freezer is leaking gas or may have another problem - It is a few years old but still works fine, but I am uneasy about giving my son something which might be dangerous.