Thanks Backaroo. I did all my ignition circuit testing in both park and neutral, so I think I’ve ruled out the transmission lockout. I attempted the ECM testing as described in the documents, but got 0v most places (I’m away from my notes, I’ll update this later). I wasn’t entirely sure the ECM was powered correctly while I had some connectors unplugged to expose the pins. However, there is no communication on the OBD2 port too. What are your thoughts on whether this also indicate an ECM issue?

Summary: I’ve proved the battery, starter, relay, fuses, and ignition switch are good. I’m confident the transmission lockout isn’t the issue. I’m seeing low voltage on the pins that trigger the starter relay, which are fed by the ECM.

I pulled the ECM this morning and ordered a replacement programmed with the VIN. I haven’t swapped one before, so hopefully this goes smooth and solves the issue.

Sounds like you have done your homework but what is "low voltage" on the relay pins? I've never had to replace an ECU. You are ordering it new? Where are you getting it and what does it cost? Yes, I think the OBD port lack of connectivity is suspicious regarding the ECU. Interested to hear how this turns out. Good luck!

I was seeing 6.5v on the triggering pins for the start relay, which should have 9-14v to trigger the start relay, which then triggers the starter solenoid.

I ordered an OEM ECM from Flagship One (fs1inc.com). They’re supposed to be tested, updated, and programmed for VIN. Price was $280. I haven’t used them before, so we’ll see.

Thanks again to everyone for your help. To close out this issue, the replacement ECM solved it. The used ECM came from fs1inc.com in about 1.5 weeks. I'm not sure how their business works, but there is at least one other site with a very similar front-end and exactly the same warranty and policy statements. Reviews are definitely mixed.

The new ECM came with an OBD2 dongle and the process is to hook up the replacement ECM (battery disconnected) then insert the OBD2 dongle, then connect the battery, close all the doors, and turn on the ignition (no start, just on) and let it sit for 30 minutes. I put a charger on my battery too just in case. After 30 minutes the instructions have you turn the ignition off, remove the OBD2 dongle, and then cycle the ignition five times. I noticed a click from the ECM each time. Then start the vehicle. In my case it started up, no lights, no issues. I'll button up the interior and go for a test drive later today.

I still have some work to do related the leak, but this was great progress.

Progress indeed. I bought a cheapo ECM from the JY to keep as a spare. When doing my research, I read somewhere that ECM swaps will work for 10 start cycles and then brick because VIN does not match immobilizer system. Internet and my memory are equally unreliable so it is a good idea to talk to a dealer.

EDIT ADD: Never mind. I saw you ordered with VIN. Should be good to go.

So far the only issue is VSC lights are on. I’ll try the zero-point process tomorrow and see if that solves it. Took it for a short drive today. I’m only at about five starts so far, but will watch for immobilizer issues.

Just to close out the issue, the zero point calibration solved the VSC lights. I replaced the sunroof with a junk yard unit off ebay with no rust and verified that the drains are both clear. So far so good.

Thanks everybody!