I used a fiberglass repair kit to fill in after using rust paint. My leak was right behind the firewall at the drivers side. My gas petal foot would get wet going down the road. Been dry for a year now.

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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car