Do it yourself and save some $. I did the plugs and transfluid myself on my 98 E320.

The cost for the plugs alone was $75. The plugs are fairly easy to replace, the difficult part is removing the spark plug boots from the spark plugs. Make sure you only grab the boot, twist to loosen and pull to remove. If you grab the wire and pull you may separate the boot from the spark plug wire. I put some dielectric grease inside the boot when I replace the spark plugs to make it easier next time to remove.

When I replaced the trans fluid, I drained the torque converter as well and used 7.3 Liters of trans fluid. Plan on purchasing 8 Liters. Keep in mind that the Mercedes synthetic trans fluid is sold by the liter not quart and do not substitute. I also replaced the trans filter, filter gasket, drain plug crush ring, and torque converter crush ring. You will also need to purchase the "special tool" to measure the trans fluid level and a new locking key tab for the trans filler cap.

Do a search for 722.6 transmissions for more info.

I don't believe shop manuals are available for the W210 cars yet.

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Ray
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles