an undersized unit is much more prone to failure, and that is, in fact, what I have noted over the years. Second greatest cause of failure appeared to be water intrusion due to poor sealing - one of the most time consuming parts of a repair job, for me, is getting the poorly designed gaskets to seal properly. This is particularly true of the newer Raymarine units once opened up. Most of the electronic circuit board failures can be attributed to water inside the case. The internal part that breaks most often is the drive belt - I carry several spares with me when cruising and replace belts as a matter of course every few years. An interesting side note is Raymarine's price on one of these belts - around $40. last I checked - that identical belt (made by Gates in Denver) is about $5. from any good supply company. They will not normally have them in stock, but can order them direct from Gates.

I also agree that a below deck electronic control module coupled with an above deck actuating rod to the tiller is a more reliable system.

I personally like the standard TP32 units for their ease of replacement underway. As I mentioned I carry two, set up on totally separated circuits - no matter where the fault is I can have a new unit in place and working in a matter of seconds. I have had virtually no problems with mine but do tend to switch units from time to time to assure myself the back-up is operable. Our boat is a 26 footer with full keel which tracks and holds a course fairly easily. As you can see there is considerable overkill in our choice of unit size and I think this has been key to their reliability.

While we are on the subject, I think the remote units are a must have should one be doing any serious cruising. I often control our boat from under the dodger or even from below should need be.