TL: DR Car looses power when cranking, months after ECU connectors got wet.

I have a 2010 G37xs Sedan. Unfortunately, I had the dreaded sunroof drain leak, which has since been fixed but I believe may be the cause of my issue. During a heavy rainstorm, water had leaked through the front drivers side firewall passthrough, and then down onto the main wire bundle. Water dripped down, and collected in the ECU connectors. Later that day the electronics decided to have a massive freakout (understandably). I dried the water, took apart the glovebox area electronics, and after drying for a few days everything seemed to be fine for a few months.

So, after that long backstory, after work I tried to start my car, and it cranked for about half a second before the car completely lost power, even the dome lights. I disconnected the battery, waited a bit and all seemed normal with the car.
The next day, the same thing happened. Both of these events were after hot, sunny days parked in the sun so I figured it might be associated with the heat.
I went out of town for the week, and once I got back I took the car for a drive and all seemed normal. When in my driveway afterwards I decided to restart the car, and it lost power when cranking again.

I believe that some electrical gremlin in the ECU is just now showing itself, and that I will have to get a new one. The issue with that is I would need to get the VIN programmed into the new ECU, which I would have to get done at the dealership. My fear is that they may not be willing to program a used ECU, and make me purchase a new one through them, which I believe msrp's at $1,600.
Thoughts?

 

I believe I should give this post closure.
After hours of troubleshooting it seems the issue was poor battery connections, that the purple contact protectant that the battery was covered in eventually collected enough road grime that the connections weren't 100% constant.
All seems to be well with my G now, if anyone has any questions with similar symptoms I'm all ears.

 

Thanks for posting what you did to resolve the issue.