My 560sel has a slight miss , which I guess is caused by a vacuum leak or a bad injector. I heard that a SMOKE TEST is sometimes used to search for vacuum leaks . Does anyone know how to perform this test?

you apply smoke to the intake after sealing off the airflow meter. it requires a tool most techs and many shops don't have. look at the link, vacutech is one of many brands and not a requirement, just for reference-

vacutech smoke machine - Google Search

good luck, chuck.