I posted on this subject about a year ago..."http://www.peachparts.com/shopforum/showthread.php?t=258037&highlight=long-gone"

When I did my head gasket (91 300E @ c220K), just around the same time you did yours, I found that there were indeed differences in head gaskets. The gasket that came out of the car was an Elring (it had been replaced previously @ about 114K) I ordered a Reinz gasket set. The gasket that came with it had an extra line of red rubber beading BETWEEN the hole for the water jacket and the hole for the oil gallery (where the notorious leak occurs).

Without going into too much detail, when I first laid the head down I inadvertently scraped a small piece of the red rubber beading on the gasket. So, I got an indie shop I'm friendly with to overnight me a new gasket. It too had the mentioned modification, but it arrived damaged so I had them send it back and get another. The new one DIDN'T have the modification and was a much lighter colored material than the ones with the modification. The warehouse said that was the last single gasket they had and couldn't get any more, only head sets. At the dealership, they had only head sets as well, but they were Elring anyway and didn't have the mod. Long story short, I tried a few online places (including here) and couldn't get another Reinz gasket with the modification. I had four head gaskets at one point!
All the Reinz gaskets without the mod were a much lighter grey material and if I remember correctly the Elrings were darker as well, felt somewhat softer and I think maybe slightly thicker.
I ended up talking to a gasket design engineer at Victor-Reinz to try and track down this modified gasket. He wasn't [if I can recall] able to expound on the darker material or could he find anything about the extra bead between the holes. But he did feel that given the location of the area that I damaged (on the outside edge of the last oil drain hole) that I could get away with repairing the small portion that I scraped off with MB black sealant. Which is what I ended up doing.

Beyond the elusive modified Reinz gasket, here are some suggestions for you from my experience:
-- Use wooden dowels in a few headbolt holes to direct the head into place. If you don't, you risk scratching the soft aluminum head on the steel alignment dowels when trying to seat the head.
-- Do not over aggressively scrape or wire brush the block surface. Especially at the notorious leak area. Take as much time as you need to carefully scrape and clean the surface without marring it. If you use a wire brush on a powered tool, use a brass brush. And BE SURE to cover all cylinders, ports and openings to not allow flying wires from the brush to get in them! Do not use abrasives!
-- As suggested by others, meticulously clean the bolt holes. Use rags first to sop up the oil puddled in them. Then use carb/brake cleaner with a spray tube (wear goggles!) followed by cue-tips and then compressed air (if available).
-- Also as already noted, check the bolt length for spec (if not new ones). Lightly lubricate the threads and mating surfaces. Properly follow the torque sequence.
-- The new style headbolts (with thick integral flange-collars) do not use washers.

Be aware that the threads in the block can get stressed after a few head gasket jobs and do sometimes strip. I believe there is even a jig-tool for installing thread inserts in headbolt holes for M103/4 blocks. It's not common but happens enough that many Benz shops have the tool on hand.