What did you pressure test? Cooling system, Iím guessing, but maybe a compression test?
If the cooling system wonít hold pressure, I would guess a warped head and head gasket failure. That probably means coolant in one or more cylinders. Be cautious of hydrolock and doing more damage. A soaked cylinder may not be an issue, depending on whether rust has started to set in. Iíd first verify that the pressure leak is in the engine, not the heat exchanger or some other external part. If itís confirmed to be in the engine, then get the head of pronto and get any coolant cleaned out before you get rust. It may not be a huge job to get it working again.
BTW, I wouldnít be surprised if this is covered by your insurance.