The new Rayamarine course computers are not compatible with older seatalk control heads. They need the ...2 model control heads (6002,7002,8002). The newer control head is needed for the setup of the course computer. After the setup is done I am told that the older control heads will work for basic control. I have no direct experience on that.

My setup consists of two autopilots, one Nautech-Autohelm 6000 (pre seatalk) and one Raymarine S3G. They are both wired to a very big switch so that if one fails the other one can be switched in in seconds. Other than the drive, these two autopilots are completely incompatible.

I have put over 100,000 miles on the type 2 drive. It has been used so long that the anodizing is wearing off the tube where it telescopes out of the drive. I always use the autopilot and have done almost 120,000 miles since I began cruising in 1992. The backup drive has been used some of the time due to plastic gears failures.

Since you have a windvane and you can use it with the engine with the tillerpilot I think you are safe without a backup course computer. I have been through three or four course computers in the time I have been cruising.

One thing I forgot to mention before is that I have also had a compass fail. The gimbaled fluxgate compass is connected with some very fine, flexible wires but eventually the wires can break from the constant motion. The newer compasses are compatible with the old ones except that they cannot be turned. You may already have the "new" style compass. If you do you can get a replacement core from Raymarine.

I suggest you watch Ebay for spare parts. I have gotten spares from used equipment stores, Ebay, and marine flea markets over the years.