Pilot Operated Valves & Jacket Service

We have a pilot operated valve on a jacket that sees steam, water and 50% Methanol in water depending if we are heating cooling, etc. We have a relatively high set pressure (100 psig) compared to the operating pressures (steam of ~ 10-30 psia, water and brine at ~ 20 to 30 psig).

We seem to have trouble with enough dome pressure sealing the system and the valves leak through the main body.

Anyone else see this before? Any suggestions?

Thanks, Ben