J.H., I presume you're smelling gas under the hood and the leaking EHA valve is the source. By all means try replacing the two green O-rings; however, I suspect the plastic case is cracked and you will need to replace the EHA valve. That was my experience with a 1991 300CE. New EHA valves are quite expensive so you may want to search online for new, or take a chance on a salvaged one.

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Fred Hoelzle