Turboed td42

Gday all.
I have just put a turbo on my TD42 Shorty with just over 300,00 km's.I didn't have any visible blow by before being turbo ed but now it is weeping oil from the turbo side of the rocker cover.
I am only running 7psi boost and a mechanic told me I need to decompression the engine by using a thicker head gasket.Does this seem correct.I don't want to blow the engine.
I have yet to have my 10mm pump tuned as I am waitng on a 3" straight through exhaust.
Any help would be greatly appreciated as I am new to turbo's.Cheers

No Way. You would be alone doing that mod mate. Are you sure it is Blowby? Seems Odd. 7psi s very very low. Factory is set at 9psi.

G'day MudRunnerTD.
I was told it was blow by.Yesterday I was towing a trailer, only about 750kg's and when I stopped there was a slight leak coming from under the filler cap on the rocker cover as well as the turbo side of the rocker cover.Its pretty warm up here and I am running 20-50w oil.
Is it possible my oil is too thick. I don't flog my car either so am a bit worried.Any ideas.Cheers