First thing I did mate, went down to 24.6 on the wet rear left...still...As a crude 1st step lower the left rear pressure by 1.5 psi to keep it around 30 psi when warm and check if the car remains stable.
To me it looks like surface overheating due to the lack of water on track. Nothing you can do pressure side. I would try to reduce rear sliding by adding more understeer to the car: more front ride height, more rear wing and stiffer front ARB. Using more aggressive TC setting would also help.
Consider increasing the rear brake duct then.definitely surface overheating due to lack of water - will try what you suggested. thanks mate