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what about the piston rings
that could be checked with a compression tester at your dealer
so for the moment course of action would include: compression test
dye to determine where the oil went, if no trace found then it could be assumed was burned; change the catalyctic converter, it went as a direct result of oil in the exhaust system
some remedial/temporary workaround includes installation of an aftermarket oil cooler with its own fan; maintain a lower engine temperature by removing the thermostat (not applicable to cold regions) and wiring the radiator fan to continously work.
Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.
Good luck and kind regards.
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