all concerns should be the same. Right off the bat, the car shouldnt be 'tail dragging' indicating SLS issues. They could be minor.

The TD is very desirable and you'll be happy to have one once you realize its utility.

I'd caution using the term 'frame' as this is a unitized body. Best refer to key areas negatively effected by rust as 'structural'.

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85 300D 3 pedal. Current project.
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.