I had the same thing on my PR12 that front leaks, it was a mess too , so Ed suggested to open a "canal" underneath the crab on the crankcase. That fixed the problem but it did took me twice to finally solved the leak. PM me if anyone need to know the details.
Today practice, I saw 4 x PR12 plus my so 5 running so it was really good comparison on performace between different setting.

A guy just breaking in the PR12 with 10% odonnel, everything stock (his engine leak little bit too) man... his engine was like "unbelieveble fast" He had the same 0,4mm head shim using 6mm stinger. Running at 110C after 5 tanks.

Our stock carb do require Warm up, it may stall and sound rich at the beginning, please keep same setting at least 2 mins before retune. Otherwise if you don't have the patience, just use Nova carb. Our carb does have more aggressive power.

Edgar, on the head shim, I tried going from 0.4 to 0.35 and was bad. Getting overheat ( no denation) within 1 lap. Try to richen and speed just dropped right away. Having see that stock PR12 ( I am definitelyt still learning ), I went to 0.45 and power was even better than before.

Today condition , air temp 20C, Humidity 59%, using 30% odonnel.

I will try 0.5 plus and let you guys know result later.