Is that a 6 cylinder diesel. Some of the earlier model were lemons, but not sure about the 94s'. Some of the 6 cyclinder diesels would warp (too think of a block). Not sure. Let's see what the pros say.

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'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)