Depends on just how "vintage" you're talking about. If you use water or water based cleaners on some of the old black Japaned finished machines with shellac or varnish clear coats the water can turn them milky white. On the other hand the newer "vintage" colored machines were painted with paint and aren't normally damaged with water based cleaners.
For the old black ones I use cotton balls and sewing machine oils. For the newer ones I try to stick to a mild cleaner.
Joe