I got most if this from an online post on one of the MB forums, and to the author, I thank you. I have edited it from my job yesterday for clarity and to flesh it out a bit. Should you see your work here, feel free to take credit, I forgot where I saw it first.

This is a pretty accurate depiction of the fluttering/machine gun door lock DIY. Hope it helps someone, the original helped me. The WIS has a little info, but as usual is pretty cryptic on details.

You can definately get the job done nicely with a "normal" manual pop rivet and tool. Only about $10 at Harbor Freight.

You don't need to take out all 4 rivets (2 top, 2 bottom) for the vertical window channel at the back end of the door. You only need to take out 3 of the 4 (2 bottoms & 1 top) I prefer to remove the one closer to the back of the door. This allows you to slide the rail out of the way (forward) but it's easy to reinstall the other rivets later. This is how dealers do it supposedly.

One more thing:

On the fronts: to take the lock actuator out you need to release and remove the door cylinder. This is held in place by one screw that can only be reached through a hole inside the door. There's a small hole just above the height of
the door latch opposite the lock cylinder on the inside panel. Mine had a black rubber piece stuffed in it. The reason you have to remove lock tumbler is there is a phillips screw behind it that is the last fastener holding the door lock actuator to the door.

The tumbler's retained with a 4mm allen {sockethead cap screw} bolt.....accessible thru the rubber plug above the lock mechanism towards the inner surface of the door.

Just replaced the drivers side door lock on my '00 ML 320. Its about $75 at the dealer. Could not find one online.

Here's my experience.

1. Be careful when removing the door panel. Use a door panel removal tool (bent tool with a forked end available at parts stores like Schucks/Autozone/Pep Boys). The plastic clips that hold the door panel to the sheet metal have plastic holders that are integral to the door panel. If you just use a screw driver to pry the door and then give a hard tug you have a good chance of breaking the plastic clip holder. Mine has several holders broken by the previous owner. When I reinstalled the door panel I purchased new clips (about $3.00 ea) from MB, different design than the original clips. The new clips work better than the old clips and now the panel is less prone to popping loose. You will probably break some. I did.

2. To remove the door panel. The wood trim on the door handle can be pryed off by inserting a small screw driver into the slot located at the bottom end of the trim piece. Remove the two screws under the door handle trim. Also
remove the screw behind the "SRS" tag on the door panel (tag pops off). The small triangular panel (sail panel) by the door mirror just pulls off. Pop out the door door clips using appropriate tool to pry the door panel. Unhook the door latch cable and the courtesy light at bottom of door.

Some write ups mention disconnecting/removing SRS airbag. Don't mess with it. You DO NOT have to drill it out, nor even disconnect it. If you power on the vehicle with it disconnected you will get SRS fault light and a reset tool is
required to turn off the light. Remove neg batt cable to power off truck while doing the work. Remember that with batt disconnect you get the BAS/ESC light (reset by turning wheels both ways lock to lock) and will have the reenter the radio code.

3. Pull enough of the door panel plastic/sound deading material out of the way to gain access. Its secured with cool resealable black goo and will peel back nicely if you are careful. Roll window all the way up. Drill out three of the four rivets holding the window guide in place. Two at the bottom one at the top. The one to drill at the top is the one closest to the door jamb and can be reached without removing the door air bag. I used a 5/32 bit to drill out the rivets and then used the 5/32 bit to open up the holes slightly to accept 4mm diameter aluminum rivets. 5/32 is too small, use next bigger size bit.

4. Unplug the lock actuator by reaching in the door panel and removing the wiring harness. Only one clip to undo here, its retention clip is toward the outside of the door.

5. Remove the two screws holding the lock actuator to the door panel. These screws are in the edge of the door where the door latch is located. Two black torx head screws.

5. The lock tumbler needs to be removed next. There is a small 4mm hex screw hiding behind the lock actuator. A good shop light will illuminate it nicely from the door openings below. Its kinda hard to see. Normal allen wrenches won't reach. I bought a set of T-handled hex wrenches. Even then I had to grind down the plastic on the handle a bit to get enough length. To expose the screw, the rubber plug in the door panel needs to be removed and the lock actuator rotated counter clock-wise about 3-5 turns. Don't go too far or the screw will come out and then you have trouble. The rubber plug is in the face of the panel opposite from where the key inserts the door. Loosen the 4mm screw and pull / wiggle out the lock tumbler. The tumbler will just pull out with some effort.

6. With the tumbler out, door jam screws out with now exposed phillips screw, and with the wiring disconnected, the lock actuator is free. Rotate the window track out of the way (slide it forward) and wiggle / worm / wrangle, the lock actuator out.

7. Install is reverse of removal. you will have to transfer the old plastic piece for the manual door lock pin (the piece that sticks up into the cabin, you'll see) It screws off and on again. I used 4mm dia aluminum rivets and a standard manual riveting tool to re-attach the window guide.

Things to trip you up, the 4mm hex behind the lock, the clips that hold the door panel on. If the tumbler pin does not line up, you can just rotate the socket in the new actuator with a flat blade screwdriver to mate up the pieces.

This is about a 3 hour job for the first timer, maybe 1-1.5 if you have done it before. Work slowly and methodically and this is definately a home DIY. No need for dealer intervention here. More time consuming than difficult.