Look everybody! A new study was published last summer of lots and lots of ladies over several years.
It it makes interesting reading. The key conclusion of interest to us was second time rounders have only a 7% chance of a repeat severe tear. Pretty good odds. I worry slightly that some of the ladies with the most severe 3c and 4th tears would have opted for sections and thus skew the results slightly. However, the large numbers involved in the study can provide us with some confidence.
Hurray for confidence!