Did your 04 wagon have it's fuel tank replaced yet? If not I would pop the driver's side cover and check it out. I bought my 04 wagon a month ago, did a bunch of work to it then finally filled it up with gas. Next morning garage reeked of gasoline, fuel was pooling on top of the tank on the driver's side. Contacted MBUSA and they said I had 4 months left on my 15 year fuel tank warranty. Took it in to the dealer and 5 days later I had my wagon back with a new fuel tank, sender, pump hoses etc for $0. Previous owner probably sold it because of the fuel tank leak, not knowing about the warranty extension.
https://imgur.com/a/6CaNUZv

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CENSORED due to not family friendly words