i have 850 NA w/ 110K. transmission shifts w/ a bang between 1st and 2nd, but a dealer's machanic said:"they all shift like that". AC is leaking slowly from somewhere-probably evap., but my regular mechanic suggested to recharge it ea year and not to replace. changed all struts/shocks @100 K, rotors+brakes and rt. ball joint/arm. plus regular oil changes and did tranny drain/refill once w/ regular fluid and recently w/ synthetic(no big change noted though). oh, little s6aff like air filter, gas filter, expansion tank cap and , of course, glove compartment lock(did that myself), thermostat, flame trap. that is about it. the car definitely has great stability and handling, ride is too stiff for me, but if the ride was softer the car would not be as stable as it is.
re your code: i'd get "a second opinion" possibly from another good mechanic or a dealer, since the code may be triggered by more then one problem