If you can get me a conditionally independent failure probability of 10^-100 per self-modification by statistical techniques whose assumptions are true, I'll take it and not be picky about the source. It's the 'true assumptions' part that seems liable to be a sticking point. I understand how to get probabilities like this by doing logical-style reasoning on transistors with low individual failure probabilities and proving a one-wrong-number assumption over the total code (i.e., total code functions if any one instruction goes awry) but how else would you do that?