I have had a coolant leak ever since RT4 in June, but it's a weird one. I only seem to lose some when under track conditions. Came back from Germany (600 miles) and lost none, and normal driving I lose none.
At JF2 I lost some again......so was getting a little concerned.
Just had it pressure tested last night, and took it to 20psi and it held perfectly. With the car running it built pressure nicely and held it.
Only possible solution at the moment is a weakness in the rad cap. So, gonna do a full coolant flush and new cap on Monday and take it from there.....will update as and when.