Mitsubishi Pajero 1999: Do I replace or keep it?

You've done the right thing to date in terms of servicing and it appears to have rewarded you with a trouble free run, so there's every reason to believe it will continue to do so. They do tend to burn oil as the kays climb, but that's usually because of an issue with the valve stem seals and is not regarded as a serious problem even though you might use two to three litres between services. They can also develop oil leaks because the seals harden over time and eventually need replacing. The cost for that is usually around $500 or so. Apart from the oil burning and leaks the Pajero is a solid performer, without major problems with transmissions, diffs, suspension etc.