Start with what needs attention that'll strand you if it breaks. Move on to things that will ruin the car if you ignore them. Then move on to things that are annoying that you can fix when you have time. Don't make the mistake of trying to do too much too fast. You'll wind up creating new problems and hemorrhaging money.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]