Go to a local car dealership and talk to the service manager. There are companies, usually one man operations, that do nothing but go around to dealers and repair seats, dashes, etc. I have had some spots repaired on some leather seats in a Chevy pickup. The guy did a nice job. He mixes the color to match, sprays it on, and puts a sealer over the top of it. This is the way I would go.
I take it that the leather is fading and starting to crack from getting in and out of the vehicle. Go to an auto upholstery shop and see what it would cost to have new side panels put in, or look up a Corvette restoration place on the net or in some specialty catalogs and see what a new set of seat covers run. This is an item you can put on yourself with some hog rings and ring pliers. Winters coming so just pull the seats yourself and take them to an upholsterers and let them work their magic. After all you stated it's a classic so keep it a classic and don't cut corners.