I do very little preventitive maintenance but I decided to change shifter cables on my Madone. I'm glad I did. When I pulled it out the cable was frayed at the end beside the cap in the shifter-on both cables. I'm guessing the cable was two years old. I opted to go ahead and replace the cables on the 5900 after seeing the frayed ends on the Madone.
It took less than 15 minutes to replace the cables on the bike and readjust the derailleurs. I also trimmed one side of the cable housing to make it look a little better.
However, it probably took me another 30 MINUTES to find the darn little screw holding the cover plate on the Shimano shifter that dropped to the garage floor when I was removing the cover to rethread the cable............I finally found it and was really surprised how far it had bounced away from where it fell..........And I thought I was using a magnetic screwdriver.