that's the one. Pull it off and examine it. If that's not it, follow your hard lines and examine all of the similar connectors. A MityVac is helpful in finding subtle vacuum leaks but yours seems to be massive and you should find it easily. Probably wouldn't hurt to replace all of the connectors as you go if they have never been. Quarter of a century old you know. Available from Phil on this site or dealer. Cheap insurance.