Disconnect the steering cables at the motor and see if it is easy to turn. That tells you if the problem is in the cables or in the motor. Unless the cables have breaks where water could get in and cause corrosion, the stiffness is more than likely where the steering arm goes through the tilt tube on the motor.
2015 Seaark 1872 MV CC Etec-90
Helix 12 CHIRP SI, HB 1199, MinnKota Riptide ST80/i-pilot Link, Bob's Hydraulic
Bitter Gun Owner