Hi guys! Im new to this forum and have had my p38 for about 6 months now. This past weekend I went to change my valley gasket as it was pouring oil. Once finished I realized I have a bigger issue as I had a bit chuffing sound and a lot of air coming out the oil fill hole. I did a compression test and have only 2 bar in cylinder four compared to 9.5 in the rest. I assume it’s a head gasket and am going to replace it. I would like to know if anyone has any advise and if I can just change the one head gasket or must do both. Cheers!