Pete, the usual checks for pools of fluid is standard even though these trucks are leaky vehicles. One a p38, first things first, check the EAS. Crank it up, listen for the air compressor to kick off 30 seconds after start up. If it runs too long, there is more than likely a leaking air bellow. Also, ask the seller at what height it was at when he parked it. If it is lower than the height it was parked at, you have a leaky bag or another problem. In short, check the EAS first to be sure that it is operational. You need to look at the HVAC display screen. See if is displaying the book with the exclamation mark. this indicates a controls issue. oh yeah, look for water (or signs of) water in the florr boards of the front passenger side. If the carpet behind the radio head unit at teh floor pan has a white residue there could be an o ring that is bad on the heater core. These are the "common" things i have had happen to me and seem to be fairly balanced amongst p38's else where too.
The SRS light could be a number of things. Have it plugged in to see what code it is throwing.
