I went a bit lower tech. I cut a hole the size of the shaft in a small piece of paper. I cut the paper so I could place it around the shaft and then marked the paper 10mm larger than the aperture and cut to shape as a template.
I took a £2 pair of black Matalan flip-flops and, using the template, drilled the shaft hole through one of the sandals. With a Stanley knife, I cut out the template shape and ran a groove around the edge of my newly formed homemade grommet. Finally I cut from one side of the grommet to the shaft hole so I could place it around the steering shaft and wiggle into the aperture.
Voila, a flip-flop grommet sealing that drafty hole.