radio buttons 2003 oldsmobile Silhouette

I have a 2003 Oldsmobile Silhoette. This weekend the "seek" button on the rear seat radio control got broke. Can just the button be replaced or do I have to replace the whole unit? Can you tell me how or is there a website I can look it up? Where can I find these parts the cheapest? The unit I beleive is Delco part # 09356849. If this is the correct part number this unit also fits in GM vans. I found a used unit for $30 (don't know if it works) including shipping and a new unit for $140 including shipping. Thanks