According to this link:
http://skinnerbox.steaky.org/Service/W124/w124CD1/Program/Engine/103/05-2700.pdf

Mercedes recommends using Viton® valve stem seals to reduce oil consumption.
Identification:brown colored material (the OEM and Victor Reinz are brown too)


Viton® links:
http://www.dupont-dow.com/literature/viton/090017a2800b04f9.pdf

Contact Viton® 1-800 853-5515 Toll-free U.S.A. and Canada
http://www.dupont-dow.com/Header/index.asp
http://www.viton.com/Header/index.asp

Here are some pics of OEM Mercedes W201- 190e 2.3 used seals:


Exhaust Valve Stem Seal


Inlet Valve Stem Seal


Has anyone used Viton® before?

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz