Rob, I know I didn't answer the question because I don't feel that I have enough knowledge with patching drysuits. In my case I was patching the inside of a trilam suit. I cleaned the area with MEK (methyl ethyl ketone) applied a couple coats of the contact cement to the suit and a few coats to the patch. The contact cement/patch stays flexible but the cement dries an ugly yellow/brown. I'll try to find a link to a video.
I understand, was just looking for your experience so far. Thanks for the post and the video.