I've had both the 12A and the 13B fuel injected version of the '85 RX-7...great cars. Both have things to look for, kind of a long list.
1. Leaking oil metering lines (the tiny clear-looking ones)
2. Excessive fuel smell in the oil, type of oil used, interval.
3. Spark plugs need to be changed annually, especially if the car was never really driven hard or run at high rpm (helps clean them out)...there are 4 of them, and they run $6-$10 each. NGK only, no exceptions.
4. Ensure transmission & diff oils replaced regularly. If this is a GSL or GSL-SE model, it will have an LSD and requires special fluid...rule of thumb, if it has rear disk brakes, it has an LSD....also usually if the car has a sunroof it has an LSD>
5. Steering looseness or clunks = needs idler and pitman arm bushings...stupid-cheap and easy to replace (put Delrin in there, don't waste time with rubber) but a great point to reduce $$ on the selling price.
6. Fuel filters and air filters changed regularly is a must.
7. Low coolant = bad. Old radiator cap = bad. Fan clutch that does not engage with in half a turn = bad. Any cooling issues, stay away...usually spells Rebuild right away, the o-rings are sensitive to that.
8. Oil smoke on startup = okay, but NOT steam. Steam = walk away. On the 12A carburated cars, you can tolerate a tiny bit of oil smoke on hard acceleration, but not on the 13B.
Both versions are very cool cars, I really liked both that I had. The GSL-SE with the 13B is a sweet car with good power, and I was getting like 26mpg on the highway with mine! Racing Beat and Mazdaspeed make a ton of great parts for them that make them fast and reliable. Suspension/struts are cheap and make a big difference in handling and daily driving.
PS-- there is no rev limiter, just an electronic buzz or "honk"....try to keep it under 9,000rpm. Also, don't rev it past 3-4K rpm until it has warmed up.