I am in the processing of purchasing a boat and would like to add auto pilot. My previous boat had a Navico system which was not much to write home about. My boat prior to that had the ST 4000 which I really liked. However, it appears that the ST 4000 has been discontinued and replaced with the S-1. I don't really see much difference between the two. Is there a big difference? It appears that I could probably buy a left over ST4000 at several locations for a substantial price difference. Please give me your thoughts. Thank you, Mike