The leather on my driver's seat back rest was worn, too, especially the side bolster.
The "wearing" or "cracking" is really superficial and can be fixed. Many guys on the forum have had good experience with the leatherique leather dye and the colorplus dye.
Check out run.exe's 500E. He completely redyed the creme colored leather in his car to two-tone gray / black with leatherique.
Also, Thomaspin fixed some bad cracking in the leather in his 300SD. He used the leather dye from colorplus, and featured the process in his website www.pindelski.com
He has a lot of good DIY stuff there, too. It's worth a look.