When you replace the plugs, be sure to examine the grounding lug for signs of crusty deposits on them. It's caused by oil, but isn't black looking, had a fairly normal yellowish-gray look to it. Sometimes also has like a "glaze" to it.
Again I really recommend only the correct plug, a local parts store may not have them in stock, unless it's a European specialty parts store. You may need to get them at the dealer. it's worth the extra work to get the correct plug. Don't let yourself get talked into a "fancy" spark plug, such as platinum tipped, dual (or more) electrode, split fire, etc, as these are typically resistor spark plugs, and this engine has resistors in those metal plug wire ends, don't need resistance twice.
At 200,000 miles I wouldn't be surprised if it needs valve stem seals. If the maintenance hasn't been paid attention to, it may even need valve guides, which is a big job. The valve stem seals however can be done by pressurizing the cylinders, no need to remove the head.