You might possibly need to replace your steering shock, or have worn out suspension components, like tie rod bushings, but the feel of recirculating ball steering is different than that of rack and pinion.

One of the complaints of recirculating ball is lack of on center feel.

I really can't comment on your feeling that the steering quality is non-linear.

I remember at first that the steering in my Mercedes was unlike any car I had ever driven, and it felt uncomfortable. It took me a while to get used to it, but now after two years, it feels completely natural.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".