Not so much a "process", I just gently take them apart, clean them up, glue the sides back together and usually make a new bottom for the case.
Then I use what ever fabric I think goes with the machine and cover the cases following the same pattern as they were originally if I can.
{
http://www.quiltingboard.com/vintage...r-t199606.html }
{
http://www.quiltingboard.com/vintage...d-t200795.html }
{
http://www.quiltingboard.com/vintage...x-t202882.html }
I haven't done a tutorial on it because I usually forget to take pics while I'm doing the work. The first thread above has pics and descriptions on how I rebuilt the bottom of that case.
Joe