So let me try and summarize Post mortem to see if I got this whole thing right:
1) leak was found following winter and filling of tank.
2) opened up and found cracked housing
3) replaced housing, pump still not running
4) replaced pump
5) pumping but would not build pressure
6) found water heater valve open, closed it
7) still not getting pressure, pump running, low flow

found valve, cleaned it out
9) everything now ok
Is this sequence right? so the leak was actually from the housing? cause? (improper winterization?) cause of lowflow/pressure was blockage at valve? Did you have pressure last year?
Also I learned something, I didnt know there is a strainer in the fresh water system, I have the same boat/diff year and will be checking this weekend.
dint think it got cold enough in Georgia to do damage although suppose it only takes one night below freezing. It why up north here i do not follow just the drain philosphy, I drain, but then I put a large amount of anitfreeze in the tank and then turn on the freshwater pump and pump it through the entire system/faucets. Cost a bit more money in antifreeze and also in spring takes a couople flushes of system to rid the AF, but it gives me piece of mind. also incredibly easy to do, no monkeying with any valves, etc.
glad it's over for you! Thanks for sharing, it really taught me some things.