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Help with E7 - 350 issues?

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I have a 99 Mack dump with an E7 - 350 and this thing has a number of issues. At first it wouldn't start and the underhood fuse block with the ECM fuse was so corroded that there was no communication, you wiggled the 25A ECM fuse and it would start. I replaced that, now it starts every time. Before I started on it, someone had replaced #2 and #5 injectors. When I went to do the fuel filter I pulled out the remains of a clump of duct tape from the housing - very bad since the tape part was already heavily broken down by the diesel and all I was able to remove was the clump of string and a bit of the rubber still connected. This might be related. The rear main seal is leaking and around the jake as are the oil filters, which haven't been changed in years, but this is probably not related as the oil pressure ranges from around 12 to 55, which I understand is normal for these E7's. There's also a tiny seep from injector 4 that wasn't there prior, but I doubt that's the issue, though the fact that the injectors keep failing is probably significant. From here it seems to have 2-3 issues that seem related but I doubt they are.

1 - If you start the truck and let it idle, after exactly 33.5 seconds, never more, neer less, it stalls. Disengaging the parking brake does not change this. I don't have a scanner, but I think there is a TSB about the ECM being corroded because of how it's facing but that comes with a 9-2 code and without a scanner I can't confirm. I haven't found the in cab module yet (anyone know where that is?) - the module on the right side of the engine has 2 clips on the top, and the clip closer to the firewall is intact, but the rear portion of that clip is cracked which may be allowing water intrusion there as well. I dont want to go too far down this road if it's not the issue. It's the precise time of cut out that is getting me, but I think that's too short for the idle shut down,

2 - If you start the truck and don't let it idle, that is raise the RPM at all, it will stay running, but then it will cut out when you let it drop back to idle.

3 - The fuel from the first fuel filter is draining back into the tank after it shuts off. This seems like a bad check valve, and my theory on this one is that it got some contamination in the valve which is holding the port open at all times. This does not cause it to not start, but you can watch and hear the fuel draining back and the one filter stays full while the other loses prime. Are the check valves in these trucks located in the filter housings?

Any help on any of these, or if anyone has wiring diagrams, ECM pin diagrams, anything. This also has odd injectors and injection pump - it looks built in and so the question there is how to clear the contamination to stop any further damage. Thanks for any help or suggestions or info.

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