distributor advance unit 1973/450sl

[zeggate]

My car gets about 6 miles to a gallon and has a miss. The cap,wires,rotor are new. I sprayed carb cleaner at the injector seals with no change in idle. I pulled the hose from the distributor advance unit and the car runs smoother. I used amityvac and applid vacuum to the advance unit ,it did not hold vacuum .Is this a sign of a faulty advance . I am not a mechanic ,Don't laugh I am just a committed DIY'er. Any help is appreciated.