Speaking of old machines, I have a great old Singer that has developed a nasty temperament. It only skips stitches when I am using it at home. When I take it in to be serviced, it doesn't behave badly. The repair man even gives me the samples and the stitches look fine.
I have replaced the gears and had the tension adjusted. I love this old machine and I have pieced and free-motion quilted many gorgeous quilts on it. Why is it behaving like this?