Water pan, or oil pan? From the title, it looks like it's your block?
Usually, depending on the location and the extent of the hole(s) producing the leakage, the order of preference might be:
First choice: replace the pan (if it is an oil pan) - call local junk yard and post a Want Ad in the Swap Meet. This is the safest and surest solution.
Second choice: if the hole/leak is small and accessible, grind it out, clean it carefully, and use JB Weld. This is the cheapest and easiest solution. I have done this to a small leak in a 261 block - no leaks in 10 years.
Third choice: weld or braze (requires more skill, tools, and/or $$$)
Fourth choice: if it is only a water-leak in the external water-jacket of your block, and you can find someone with the equipment and the expertise: better than brass-brazing might be to grind/prep the metal and
spray weld the crack in the cast iron. I recently had this done by a retired engine rebuilder. He told me that he could use this method to repair a 20" water-jacket-crack in the lower edge of 235 block that I also showed him.
