I have a #3 and in most cases haven't had any trouble getting new parts. For "insurance": I recently replaced the prop shafts with new "monster" shafts, which were custom made. They were less expensive to make and are _much_ stronger than Merc's large shaft (NLA).

One note about dimensions: I think that there are differences in 3,4 vs. 3A,5 gimble and trim ram pin diameters.