Hansa
Probably a Hansa Rondo, and the vacuum breaker inside the spout is leaking. They don't make a replacement vacuum breaker, but you get a brass plug to replace it. Getting the old one out can be challenging because it is at the rear where you cannot get to it. The easiest way is to take the cartridge out, (you probably should get a new one at the same time as the plug), and push the vacuum breaker out from the inside.