1997 Subaru Legacy duty solenoid

This car makes almost groaning noise when turning hard right or left at a slow speed or backing out and turning at a slow speed. I have been told by the dealer after an independent repair shop sent it to them because they could not figure out the problem that it is the duty solenoid in the transmission. Apparently all the wheels are engaging even when it is not necesary. The repair is in the $900 range. Do you think the repair is reasonable and with the age and the mileage of the car do you think it is worth a $900 repair. Can the car continue to be driven in this condition or is it a hazzard? Thanks