Replacement shifter parts are all available from MB when I rebuilt the entire shifter internals in one of my 87 300E cars (it had about 230K on it then) it restored it to perfect condition, it was perfectly tight with no slop whatsoever. Parts 8 or 9 years ago where about $60 as I recall.

If you do it right you won't be disappointed. New bushings on the tranny shift arms and shifter arms should be replaced as well of course.