Thanks for the responses. I use a small brush to even out the solution after I coat the paper with a glass rod. Brush usage is VERY minimal. The brush does have a metal ferrule. I assumed it didn't really matter as long as no metal came in contact with the solution. The paper isn't being cut by me, it's pre-cut 8.5x11 Crane's kid finish.
I'll give it a try with a Hake brush and see if the rust spots still appear.