Saddle sores = worn out saddle?

Did St. Anthony's this weekend and came away with something I almost never get: a saddle sore in the nether region.  (I'd post a pic ... but you don't want to see it! )

I did not apply chaomis butter or body glide prior to the race .. but I commonly do not do that before most races.  Plus, the ride was only 25 miles long - and there was no swim.

Tri shorts used were some that have been tried and true through other rides with no problems.  Saddle was in the same position as were the cleats on the shoes.

This leads me to think that perhaps maybe the saddle is wearing out?  The leather shows no scuffs or means to rough-up the skin ... although it does show wear as I have put somewhere in the negihborhood of 4500-5500 miles on it since 2007, inlcuding all the way through IMCdA and IMFL training (the long rides of both did not produced saddle sores like I got  from St. A's)

Question: how long do saddles last?  How often do you change out your saddles?