Would anybody like to share some tips for how to properly clean and care for older speakers? Or, link to articles that speak to the issue..

I have an early 80's pair of SS-U560's. They're great. But since they're getting up there in age, I was wondering if I can treat them to protect from getting dried out, etc. Can a substance be applied to speaker surrounds/cones to keep them in good shape and prevent drying out?

Thanks.