"it would be interesting to know just how much of the Falcon 9 had to be rebuilt for this launch."
In the press conference afterward Musk on YouTube said they kept the main structure and engines but replaced anything that could be removed and looked a bit iffy.
They will no doubt now remove all those parts to see what a first flight has done to the parts they replaced.
Around about the 18-20min mark Musk says they expect the first stages to have a life of 10 launches with no refurb and a 100+ with moderate maintenance. So at 10 launches the TPS could have definitely burned through somewhere and the TEA tank (used for engine ignition) need refilling (the SR71 used a similar igntion system and the small tank was good for about 5 starts IIRC).