It sounds a lot more than just the stat tbh, the best sealant to use is the Loctite one sold in Halfords, as easy to get but long term buy yourself some loctite 5900 or 5910.
The obvious excessive pressure is normally a sign of a duff head gasket though.
If you use a cometic reuse able stat gasket don't use any sealant it's not needed.
tabetha