Apologies for the wordy explanation, but there may be clues for those of you who know about these things. Thank you for your time.

First potential symptom was intermittent check engine light (solid, but not always on). Then car broke down, rpm's dropped to 500, no power for 5-10 seconds, then engine shuts off. Cranks, but won't start, green key flashing (immoblizer). Tow it to a mechanic. Mechanic baffled; no codes and no real communication with car either. Doesn't know what to do, but pokes around a little and the car starts. Drive it for a few more days, then on the highway, full/instant engine cutoff. Coast to stop. Cranks, won't start, green key flashing. Push it a bit, it starts. Drive it home and park it. Next day, drive it to mechanic, drives fine, turn it off. Won't start for mechanic. Locksmith comes to try to communicate with immobilizer, etc., can't get anything from the car. We check relays, ignition coil, still no start. Mechanic gives up, I tow it home. Still cranks but won't start. Rather than give up, I decide to buy a used ECM to see what happens. Remove old ECM and notice evidence of damage in connector E (pictured below). New ECM comes, I install it, locksmith comes and does relearn, car starts. Driving now for over a week, no issues, no codes.

Does this seem like a failed/bad ECM and I should just smile and drive, or a short /bad ground that fried the ECM likely to just happen again that I should try to track down? From ECM picture, the problem was potentially in vicinity of Connector E, pins 19, 20, 21, 29, 30 (I think 31 is empty). I checked a couple of the pins in the connector and they looked fine...no corrosion, etc.