I would look into using JBWeld to re-make the controller housing box. I would think about putting in new threaded inserts in there before you start, so the screws can grip nicely. An alternative would be to put the screws in there before you JBWeld, then take them out before it sets. But, I would think my first approach better.
Since everything might not fit perfectly snug, I would suggest keeping the gasket, but also using 100% pure silicone around the controller box when you reseal it.
As for the missing parts, there are a number of people who part out boards on Reddit and FB, try posting there.