well for now at least...
it took:
- new rear main seal
- new front & rear PCV valves and gromits
- new oil adapter O rings
- new oil filter
- re-tension the sump bolts
- replaced welsh plug
- re-soldered radiator inlet
- new thermostat and gasket
- new heater hoses
but my XJ hasn't dropped a drop of oil or coolant for the last week!