For a 7m, look to checking and replacing all old, cracked hoses, run a compression test, leak test, check the CEL for error codes, check the block above and below for fluid leaks, check the LSD in the back for leaks, ask questions like... "When was the brake pads last done/replaced?", "When was the timing belt replaced?", "Have all the other belts/pulleys been replaced?", "When was the last time someone replaced the spark plugs/wires?", etc. Check the engine for pulled cables/wiring/big gaping holes in the engine bay where a component used to be. Get the VIN and Carfax it to check things like maintenance schedules, accidents, etc. Check the tires for severely worn tread/uneven tread/numerous patches. Check for RUST. Take it to your local mechanic BEFORE buying it and have him inspect everything as well.
It's just like any other used 80's ~ 90's car. Know what you're getting into before getting into it. Don't be swayed by flashy mods like LEDs, engine chrome, turbo timers/boost controllers, pillar sway bars, nose/skirt/rear fender/bumper jobs. And if the OP says anything remotely similar to FCD or Fuel Cut Defencer, RUN, unless he replaced the ENTIRE fuel/air system. FCD is bad juju and can lead to BHG's and other nasty bits.