Sorry to be a smart ass here, but it is the 2.8 engines that are prone to head gasket (usually around the EGR valve) and fuel pump seal failure, 2.5s are pretty sound all round. I've had pajeros for the last seven years a 2.5 and a 2.8, very good, capable and comfortable cars. Auto box is better as the sychro hubs tend to go in the manual box (what killed my 2.5 - £600 for a gearbox refurb).
Well worth getting on the Pajero Owners Club forum @ www.pocuk.com/forums. Been a member there for well over 6 years and found it to be a great source of info. Banter is good too!