The rollers themselves don't look completely smooth anymore, and anything that chips off the rest of the surfaces can get stuck between rollers and film and scratch. They can also get sucked into the bellows and onto the film surface by vacuum when the camera is opened, causing black spots on the picture. I wouldn't be surprised if the bellows already contains more particles than the rest of the camera, they usually do. A thorough clean and blow out at minimum is a good idea with any old folder.
I like Rustoleum black oil-based metal paint for those types of things, takes a while to dry but makes a hard surface. You may have its equivalent in the UK. You'd want very thin coats of paint no matter what you use.