We own a 1995 Hunter 336 and I noticed one vertical crack (about 3 inches long) at the base of the mast shortly after the purchase. It looked as if it had been there for a very long time and did not seem to get any longer over time. I figured that it might have been caused by some stress due to sail force against the mast.
I did not try to get it fixed or soldered. Instead, I had a SS collar made (about one inch wide) that circles the base of the mast. The collar is held thight by a SS nut and bolt. It simply makes me feel good.
Hope this helps!
Good luck.