I would inspect all the calipers, may have got the brake fluid too hot. Brake fluid can buiild up moisture and in extreme braking that occurs racing you can acually boil the fliud. I would check all the calipers, if the fluid got hot enough the seals may have been soft upon loading the car, as the system cools and the seals around the calipers cool then the seals are no longer expanded they tighten around the caliper pistons and do not seal to the housing. May be why you didn't notice it till later. Although it could be something else. I would check the seals and pistions on the caliper, and empty the system of the old brake fluid, flush it through with new till crystal clear. That would be my approach to start.