Diesel Giant has a good write up on changing them, although he managed to do it with the intake in place.

I thought that I could do it as well, but my intake is going to need to come off. I was able to do the #1 and #6 so far, but that is it. Helps to have a swivel socket!
Unfortunately for me, three of my intake bolts are stripped (my own fault) but within the next week it WILL come off!! Then I'll get the others.

Basically, just unhook the battery and for each plug you will need to first unscrew the GP wire nut, which I believe was 10 mm (or around there) and after that is off, you can undo the plug. Mine didn't give me any trouble coming out. It's pretty straight forward, I'd say the worst part is getting the manifold off / contorting yourself with it on. Be careful not to drop anything into the engine bay, like I did with my reamer. It is not sitting lodged into a crevace next to my starter.

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k