Problem with car

Oil is leakng into the plug tubes from the plug seals under the valve cover. When the spark plugs are flooded with oil misfiring would occur, causing the vibration.

It is not too difficult to do the job. All you need to do is to remove the rocker cover and you can replace the seals.

A ring problem would fouls the spark plugs but not soak them. Bad rings would consume oil but not leak out. Whoever told you that is not versed with the engine. Only external leaks can soak the plugs. If the leak is minimal, it would take some time for the oil to accumulate. If you dry out the oil, there is a possibility you can still drive around without any problem.
A temporary fix is to remove the rocker cover and clean the gasket and reinstall with a thin layer of gasket sealant in between.

You're welcome. Likewise valve seal problems would be similar to bad piston rings, consumption of oil with emission of smoke, especially when starting from cold. Oil would not leak out. If you look closely, you should notice oil around the plug wires and tubes, indicating hardened plug seals. Foreign cars work on the same principles, just that designs are different and being not familiar means you might be slower with any work on them. In fact Japanese cars are rather easy to work on as they are quite mechanic friendly without the necessity to remove too many components to get to one, except accessibility might be hampered by space constraints.