I had these exact same symptoms, and after searching around and asking the very same question on the UK-based Pajero owner's forum, the consensus was the same as what you're hearing here. Injector pump seal on the input shaft.deli1733 wrote:Ive been having an issue with my pajero stalling about 5 minutes after it is started, it has been getting worst, it was usually when idling now it does it when im driving. the batteries were bagged and i thought that was the problem so i replaced them and its still stalling. Im not driving it right now but ive tested the alternator and its putting out 14.2 volts. I bought a fuel filter yesterday so ill try that. Im kind of thinking its the front seal on the injection pump but not really sure because it starts really well in the cold with little to no smoke. Any ideas?
I had a local diesel mechanic do the work, and the part was sourced locally as well. IIRC, the total bill was about $300 for the labour, parts and taxes.
Here's the seal they removed and replaced (punched and drilled for extraction):

And here's the exploded parts diagram showing the part in question circled in red:

Since having the work done, the Pajero hasn't stalled once after starting under normal conditions. I forgot to plug it in one night at -35 here in Prince George, and it stalled once immediately after start-up, but no more of the usual "run for 5 minutes then stall for no reason" nonsense any more at all.
Hope this helps!