There is a value question separate from price. An 84 SD and a 92 2.5 priced the same - everything else being equal, the SD is overpriced or the 2.5 is a steal.

How much documented history is available for each car? How recent is complete suspension work? Any records of major transmission work? Do all the amenities function per the owner manual, particularly the AC?

Do you have details and documentation on the 2.5 rebuild? There are few hands most of us here would trust to properly rebuild an MB engine. I'd ask why it was rebuilt. A 2.5 chain can snap requiring head work and possibly new pistons. The turbo boost system can malfunction resulting in low power and an opportunity for a questionable shop to recommend a rebuild. I'd almost prefer they continued the ruse and not actually touch the bottom end than cut corners and shorten the life of an otherwise good engine.

Sixto
87 300D