High Pressure Oil Leak Repair/Other Bullet Proofing - Question on Cooling System

[the_mig]

Hi Folks - Newbie to the forums so here is some background: I purchased my 2005 6.0 in May 2011 with barely 24k on it. The prior owners were retired and had planned to travel but never used it that much so it sat in the garage - it literally looked show-room condition. Over the past year, I put 20k on it with about 20% of that time towing boats and snowmobiles. Love driving my "red neck limo".

In January 2012, I started to develop the no-start-when-hot issue. I took it to my friend's auto shop and he scanned it and found 128psi oil pressure when hot cranking. FICM, fuel pressure, and other readings good. I've started disassembly and found that the STC fitting has failed. I'm also doing some of the other bullet proofing including dummy tube and stand pipe replacement, EGR delete, oil cooler replacement, coolant filter install, turbo oil delivery tube, and "blue spring" fuel pressure regulator upgrade.

Wondering if you all could weigh in on a few questions:

1. I didn't do a coolant flush prior to disassembly, and to the best of my knowledge there hasn't been one done in the 7 years/43k miles. Now that I'm putting in a new oil cooler, I've read some of the posts about flushing before install of the new oil cooler. Any thoughts about pre vs post flush?

2. My degas bottle has some dark residue in the bottom. I've watched several videos and looked at pictures of degas bottles that don't appear to have this residue. The coolant looked good when I drained it and there is no sign of off-gassing from the cap, only this dark residue on the bottom. EGR, turbo exhaust pipes, and oil look good with no sign of coolant leak. Any potential causes of the dark residue that I should check further before I start reassembling? I've attached a couple pictures that hopefully show the residue.

3. With only 43k on the engine and no indication of high temperature issues, I wasn't planning on replacing head gaskets and studs at this time. Mistake?

Thanks much for everyone's time...