As I recall back when I had the issue I had done a complete flush before the season started, and before that event, then that afternoon at the event (after the incident).
After that weekend I flushed it again - only to switch brands.

Since I switched to AMSOIL DOT4 brake fluid, I flush and bleed drastically less than I ever did with Motul. I just don't feel the need. The pedal stays hard where with Motul it'd get a bit spongy at the end of each session. I'll never go back.

 

^ I'd be curious to see your results if you did switch back. I just ran the AMSOil brake fluid for a weekend + 1 additional day last week. usually I run RBF 600, so this was my first time ever on the AMSOil stuff. I wasn't really pushing the car hard the frist day (shaking the dust off), but after each session with the AMSOil my pedal would be soft. It would get hard again by the time I went out for the next session, but that wasn't a confidence inspiring feeling towards the end of your session. With motul RBF 600 the pedal seemed to stay hard all the time and I know when I was at the track last with MOtul I was driving the car much harder than I did these past 3 days...

 

^^ Sounds like the opposite of me.

Tell me this though - you say you weren't driving as hard but what about your braking. I know when I'm driving 7/10's I'm actually heating up the brakes more. Be it I'm on the brakes more to slow down the car, just sloppy; whatever.

On my hot laps where I'm really pushing - I use the brakes less overall. And I've got data I bet that proves that. A hard jab won't get them up as much as a sloppy slowdown where your braking about 70% for longer. Make sense?

 

I know what you're saying, but if I'm running 7/10ths then I'm only braking 7/10ths. I always try and keep my braking hard and short, as it should be. I don't sit on them for extended periods of time and I don't use them lightly.

 

I had a similar issue with my Motul brake fluid, but get this. I used an unopened bottle of Motul that sat around for over a year, went on the track and boiled the fluid. I refused to switch fluid thinking it had something to do with not having brake ducts. I flushed my entire system and used a new bottle I purchased; I never boiled the fluid the whole day. I think the fluid I used before sat around too long. Just my theory.