I use a small rotary wire brush to remove surface rust, then treat all the springs with a rust inhibitor (Dinitrol AV30) that dries to a firm wax.
If the rust is deep then you run a greater risk of the spring suddenly snapping, especially if that rust is at the most stressed area, near the post. Replacement may be advised.
It is common for all the springs to start rusting on top quality saxes in non-Arizona climates within a couple of years.
A good case for well-designed, high-quality, stainless steel springs. It is VERY rare for a stainless steel spring to break, because they do not have the same brittle quality.
I suppose the manufacturers are obliging an archaic perception by some players that steel needle-springs are in some way better.