Its very normal. All 5 of the boats I have dealt with over the past 15year all have done the same. Most have been Morse cable systems. Some steering systems have a screw cap with O ring to seal around the steering shaft, that you attach on the noncabled side at the shaft exit point. This can help keep the greese in and dirt out, however generally I think greese on the transom is expected. I just give it all a clean occasionally normally when I service that area.