Yep sounds like a vacuum issue to me as well, I bet cleaning the system as posted above and correcting the vent leaks will make it good to go. One thing to keep in mind, however, even if the a/c is charged fully with r-12 and everything is working perfectly, it simply won't have the cooling power of modern cars' a/c. These things are going on 30 years old and new technology really provides improved creature comforts.