Quick question about the block

So, been doing some refreshing on the Dart to get her back on the road. Been a few years as things have come up. While checking out the driver side of the block, I noticed a hole that had some fluid in it. Is this normal? What is that for? Pictures attached. Also, noticed a nice crack in the exhaust manifold. I have a supersix intake I want to put on soon so now thinking of going with some headers since this exhaust mani might not be salvaged. I do have a mig welder, any tips on welding that cast iron?