100k is what the manual states. I brought it in for this at about 50k, and the service advisor at the dealer said to wait until 100k. I did and all was well.
Just as a preventative measure, have the thermostat replaced too.
If you are going to have the plugs changed at 100k, then you better pay someone to do it. I changed mine at 35k and they were a pain to break free then. I couldn't imagine them at 100k.