Funny enough I have the same problem, I bought 1999 gtb about 2 weeks ago and the first thing I noticed was the steering felt funny. the steering felt light sometimes then heavy and when you turn the steering wheel it jerks back to centre. My wrx and forester never did this. I noticed the previous owner had way too much power steering fluid in it so I removed some and also changed fluid, it helped a bit. I had my mechanic check the belt and pump and he said they were all good and this model does have quite a light steering feel.