An easy job. Leatherique makes a very good dye (leatherique.com). There are also lots of other comparable dyes suitable for your job, so this is not a unique product by any means.
I think you'll find vinyl to be a much better candidate for your task than leather. It's more durable in the long run. You'll also probably want to do both seats in their entirety just for uniformity.
Douglas Kim
New York, NY
280 SL #016220