It really is a 5-minute job, and the instructions linked above really help.
The part #'s for the various bulbs are not on the diagrams you can find at OEM parts sites, but the parts person at a dealer has a way to see them.
I just had to change 3 of mine in my new-to-me 4R. I removed the unit in the dealer parking lot, carried it in, and pointed to the ones that were burned out while the parts guy had the right parts screen up. They did have to order the bulbs, and they were ~$6 each.
Other forum members have bought bulbs from Radio Shack, and then have to swap the bases over.