What ever model you buy make sure the evap core has been done, every W140 will go through one at some point. $3k job. I6's had weak headgaskets, also you mentioned 94 that would have the bad wiring harness. Just find the best taken care of example you can that has had all of the above problems taken care of. I would still be ready to spend a few grand a year keeping it up.

W140's are nice cars but not for the faint of wallet. Since you mentioned the word "budget" maybe a mint 1991 560SEL?

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200