Spark plugs in the M96 engine need to be replaced annually. While you’re there, you should change the spark plug tubes as well, especially if you have no record of them having been changed. You can do it without dropping the exhaust first, but it will take you twice as long, even accounting for the time it takes to drop and reinstall the exhaust. Wayne Dempsey has a good DIY for spark plug replacement so we don’t need to repeat it here. Having done it both ways, I will be dropping the exhaust from now on. Be sure that the engine is cold before you begin.
If you find oil on the inside of the tube when you remove the plugs, then the tubes have cracked. Why else change the tubes? If you find oil on the valve cover seal or what appears to be a head gasket leak without an identifiable source, then your tubes may be leaking due to worn seals. They are relatively inexpensive to replace, and can help prevent wasting money on a more expensive repair that doesn’t work. The part number for the tube is 996-105-325-52. (Be sure to get the O-rings as well.)
The trick to getting the tubes out is to find a Porsche plug tube puller tool (expensive) or use a (cheap) boat plug. Tighten the boat plug using pliers and pull the tube out. Lube the sealing rings with dielectric grease and just press them back in. Replace the spark plugs without anti-seize compound and away you go. This would also be a good time to replace the coil-packs if you have no record of their replacement (997-602-107-00).
Since we dropped the exhaust to work on the plugs, we decided to upgrade while we were there. (Caution: rationalization in progress). Besides, the stainless steel exhaust is a thing of beauty and quite a bit lighter than the stock exhaust it replaced, which had started to rattle in recent weeks. Installation is very simple provided that the exhaust flanges haven’t rusted too badly. We replaced the cuffs, bolts and nuts all around. When we got the old exhaust off the car, we found out the internals on the right side were just floating around in the can — there’s your rattle.