The power plant is rock solid. I have seen one grenade-literally, it threw a connecting rod through the side of the block, but this was a manual transmission, and as far as we or MNA could discern, he probably downshifted instead of upshifted, the errors in the engine ECU (Motronic) were flagged at 8900 RPM!! Other than that they are prone to oil and coolant leaks, usually the front timing cover, oil/water pump and cam covers, I have replaced head gaskets once for an oil leak. I have replaced four or five and rebuilt two for hydrolock from water ingestion. By and large mechanically they are VERY sound.
If the AC system is leaking and needs a recharge annually, it is most likely from the expansion valve o-rings.
The check engine light will only come on if it sees a problem, which might only be stored and not present, however THERE IS A PROBLEM, it is probably being misdiagnosed.Purchase an aftermarket trouble code reader and clear the errors, if they persist, take it in for servicio.
Oxygen sensors should be replaced every 4 years regardless of mileage.
The BEST part in the car was handbuilt by you know who.