There comes a time when the boots need to be refinished, or replaced. One of the speakers at our Oklahoma gathering was from BOOTS EDGE, a company that refinishes the boots. They have a toll free number 888-687-0945, and I would suggest calling them. Your mechanic can restore the boots, but there comes a time when you actually need to replace them. Bootsedge.com can do that as can
http://www.deicerboots.com/
The latter place is the home of Goodrich, the folks who actually made the original boots. They have some publications that can help with your decision.