Since we added a wind instrument, we replaced the stock speed and depth instrument  heads with a  Raytheon  Tridata unit.  The new instruments were Series 60 types with  gray cases.  The original  ST4000+ Auto Pilot had the series 50 black case.  Raytheon provided a new gray case for the Auto Pilot and installed the latest software upgrade.  Raytheon has been very helpful with advice and support. AUTO PILOT THOUGHTS - A wheel mounted auto-pilot is not strong enough for long periods of sailing under high winds.  Both Bill Hemena and I were aware of this problem because of our pre-rally off-shore trips.  The unit on his Catalina 34 failed on our return trip from Charleston and mine had failed in heavy weather on the Albemarle Sound.  Fortunately, on  the Bermuda trip we carried Bills drive unit as a back-up.  The unit on Full Moon began to fail as we were approaching Bermuda.  During our lay-over we replaced the internal belt and assumed all was well.  Approximately 10 miles out of  St Georges, on our return trip it began to "kick out of  gear" again.  We replaced it with Bill's unit which performed well for the return trip.  When I sent my unit to Raytheon I was told that it required some tension adjustments that are not described in the manual.  I don't blame Raytheon -- the unit is simply undersized for serious off-shore sailing.   I am going to replace the unit with a Raytheon ST5000 linear drive model.  Replacing a wheel mounted auto-pilot at sea highlights the need to make sure, before you depart, that your emergency tiller works and your wheel can be removed easily.  Fortunately, we had checked both before we left.  I had to use a puller to get the wheel off.  From now on I check it at the end and beginning of each season and keep the shaft greased with a Lanocote.