My post that I did a while ago might be helpful:
LINK to Spark plugs and wires replacement
You don't have to remove the valve covers, I was replacing the gaskets at that time.

 

With the freeze-spray, it went far better than I expected. I was dreading the snap of a spark plug shattering, or the grinding as the threads tore out. I have really been worrying about this since the 50K mileage mark, and thinking about it for the last couple of years. I will change them at 50K miles for the next change. But I also put nickel anti-seize on the plug threads, so don't expect a problem the next time. I expect it to be far more routine the next time, and I have all the special tools for it now. So my mind is far more at ease about it.

When I removed the plugs, they did not look appreciably different than the new ones. I assumed they would be eroded or damaged in some way but there was nothing apparent. They also were not covered with any buildup, which is what I thought might tear out the threads as I removed them. They were ALL a uniform tannish color. Once they broke free, they all unscrewed quite nicely, and after the first set of 6, when I knew my technique was working, I was MUCH more confident on the opposite set of 6 plugs for the driver's side. The engine apparently burns VERY cleanly, so I assume MB has the injection, and engine computer very well tuned to the vehicle.

I did the passenger side first, as there is no need to disconnect the fuel line doing it. I wanted the LEAST number of complications on the side I started with, as I was anticipating trouble with the plugs the entire time. I didn't pull the valve cover on the driver's side, as there seemed to be no real difference, and when I tried the first plug on the driver's side, it was apparent that the removal of the valve cover was not warranted. The first side took me nearly 8 hours to remove the valve cover, change the plugs, clean the valve cover and reseal it, and put it all back together. Just doing the plugs on the driver side, took me about 2 hours total for everything, since I had learned a lot doing the first set on the R/H bank of cylinders.

It WAS nice to see the valve gear on the R/H side when I took the valve cover off. The valve mechanism looked like new, with fresh oil all over it, very clean, and no dirt or other signs of wear or damage. The synthetic oil is apparently doing it's job very well. After seeing it, I believe I might get 300K miles out of this car, which would be wonderful. When I am working on it, it makes me grumpy, but when I am driving it, it makes me smile. I am still annoyed at how much maintenance this car takes. With the Jaguar, I expected it, but the Jag was so nice, that after I had driven it for a week, I no longer cared that I knew it would be high-maintenance, and I was never grumpy about that. If I was in a bad mood after work, by the time I got home, immersed in the leather and wood and delightful driving atmosphere of the Jag, I was always smiling and in a good mood. As I said, THAT is what you sign up for when you adopt a British car, and like having an extraordinary housecat that pesters you constantly, it is enjoyable even though unpredictable. The Crossfire is less of a character, and very efficient, but not as delightful as the Jag XK-8. But I still like the Crossfire. The Crossfire's German engineering shows up, such that when you change a part, the problem is fixed, and stays fixed. So there IS that!