It looks like a few things changed from the earliest Santorins..
The whole C drive is different - inside and out. I may well be wrong, but it seems that they may have put the SM C drive into the Santorin; mine looks just like the SM. I don't know if the later Maramus had this type of C drive?
Again the bow roller has been modified on later models. The main chain channel seems to have been moved more to starboard on my boat, the forestay chain plate now being right on the centre line, and an extra bow roller attached to port of the forestay and bolted on to the main bow roller. The fibre glass bow profile is now no longer off-set. The cracks will be stress cracks from the boat sheering at anchor or on a mooring caused by the pressure on the S/S side plates of the bow roller. I'm pretty sure this is just cosmetic (I'm not a surveyor!).
Again, the rudder hinges look different.
I'd be interested in the evolution of the Santorin looking at your photos. The Maramu stopped production when the Super Maramu arrived, but the Santorin started production a few years after the SM. Although the hull/deck/interior design is so similar to the SM perhaps some of the mechanical parts were initially taken from the similar sized Maramu? Then at some early stage it was found that SM parts could be made to fit the Santorin, streamlining production costs??....
Bottom line though, as Mark said, don't pursue further without a survey from a someone who really knows Amels - an older boat is always going to need available spare parts.
Ocean Hobo - SM96