YEa,

That's a big mess! I've done a few of those cars. Cleaning the dash with a good spray cleaner- I think last time I used westly's wheel bright or something.
Throw away the old insulation on the leg well closeout panel and buy a new one ($25 from Mercedes). If the carpets are oily, I would see if you can't find a few used ones.
I would make sure you get up the oil so it doesn't get into the tar layer under the carpets. I've replaced them to get the oily smell out of the car. Not hard, not expensive-but it will take a few hours.
Remember the front mats are higher than the rear- so make sure you soakup anything that heads toward the passenger seat.

TSP is a good idea- Where do I find it? SAMS? COSTCO? Industrial supply company? Restraunt supply company?

As far as oils- that's probably the most loaded question on the list. I would say Delo 400 15W40, noting that Mobil 1300/Rotella are good products. If you want to go synthetic... that's another ball game. Dextron III and I node the preference for Chevron brand due to quality over some-noname house brand.

I've done this several times- so shoot me and email if you have questions. I'm leaving for 4weeks on Christmas.

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E