Whilst digging around under the dash I found that the original sound proofing wasn't doing its job anymore.  The factory sound proofing was a mix of heavy molded rubber parts and felt/tar panels that were glued to the fire wall, tunnel, door skins, etc.  The glue hasn't stood the test of time, at least not on my 96.  Some had completely fallen off, others had peeled back to the point of uselessness.  Time for repair.

After some web research it seems like the most cost effective soundproofing is this roof tape.  Easily found at Home Depot (and may other places, I'm sure).

This stuff is a tape form of the rubberized asphalt mats (think Dynamat) that are so popular in the car-audio world.  It is a bit thinner which makes it easier to apply and wrap around bumps, and you can layer it as much as you want.  It is insanely sticky, though you will need to remove any dust and loose debris before applying. 

After ripping out the last bits of the old stuff, I applied 3-5 layers of the of the tape, making sure to bond firmly with the sheet metal.  Some of the peeling felt panels were too hard to get at.  Cutting off the peeled part and then bonding the rest down with more tape seemed like it would work for the long term.

End result: noticeably quieter drive.  Motor noises are softer and more of a hum.  Of course, that just makes the wind noise around the A-pillar that much more annoying.

I also applied some inside the door panels.  For the door right above the exhaust outlet, I taped over the drain slots and then poked some smaller holes.  Probably not a good idea in rust country, but fine for sunny California.

Should have attached this.  It is for my particular VIN, but it is probably very similar to any W463 with an underhood electronics box and the battery in back.

That is probably the rubber seal around the steering linkage.  That same part on the E-class failed.  It took a while to figure out why the car would get rhythmically louder/quieter as one made a turn.  Not a lot of fun to fix on the E-class.

If you are talking about your G, that steering shaft seal would be for the 2001+.  On the pre-2001, I'd check the big cable duct to the outside of the brake booster.  If it has cracked, or opened up, it could leak a lot of air.  It would be nearly impossible to replace, but a closed cell foam plug would work just as well if not better.

As far as I can tell there are two sources of roof noise:

1) A-pillar noise from air going around the vertical rain gutter

2) Sunroof noise caused by the seal going bad.

From your description, I'd bet on #2. Try taping over the sunroof gap and see if it goes away.  Mine came with that noise.  I think the PO left the sunroof in the pop-up position for long periods of time.  The rubber is easy to replace.  It is a W140 part, where there are two types one for the glass sunroof and one for the metal sunroof.  For the G, you need the metal version.

EDIT: no odor that I can tell.  If you smell the edges of the stuff it does stink of asphalt.  The aluminum sheet effectively locks that into the material.  I suppose you could always leave a roll of the stuff in your car and see what you think.  Note that my G doesn't exactly have that "new car smell" to begin with.