no reverse 92 legacy sedan 4EAT transmission

How many miles on the transmission? What does the fluid look like? Brown or red?

Don't think a trans fluid flush is going to fix this one, and I doubt it's worth taking it apart to chase a torque converter or errant solenoid at this age. But if the fluid's clean maybe dropping the pan and looking around is not too far-fetched. Good luck. If the balance of this antique is worth it I'd chase a used 4EAT, as there are plenty around. Can't remember if 90-94 used an external reverse sensor switch too. That'd be easy!