I would also look at your valve adjustment. On these engines it tends to decrease due to the relationship between the cam and the valves. As the valves wear, they sink deeper into the head and your clearances become zero, and sometimes even keep the valves open a tad. This reduces compression in the cylinders. I have had several that would not even start, and all I did was adjust the valves.

I have one with over 300K on it, and it does its own little "dance" idling especially when warm. I know I have a cylinder with low compression and thats whats causing my wiggle haha.

Also.. another sin all Benzes suffer from.. is odometers that fail, work intermittantly etc. Unless you can document your mileage, you may have more on it then u realize.