MyOtherCarIsANissan

Hi Guys!! I'm a newcomer here. It looks as though I' not alone with my head gasket issues. Have had a 84 720 KC 4x4, since 1989 (45,000 Miles). In 2010 at 169,000 miles, seemingly out of nowhere, the head gasket blows between #1 & #2 cyls. Had the head milled with valve and guide service as well. Very carefully reassembled using Fel-Pro gaskets and Factory Repair Manual for specs. Adjusted the valves and retorqued the head bolts at 171,000 miles, then at 175,000 miles. Now at 181,000 miles, after running magnificently for 3 years, the head gasket is blown between #1 & #2 cyls, and again, seemingly, out of nowhere. Drove to the grocery store running fine. 20 minutes later, it started with a loud rattle and severe miss. A compression test showed 75 psi for 1 & 2, 180 psi for 3 & 4. While disassembling, the head bolt torque did seem to be loose, though I did not test them for torque . My questions regard what I found after disassembling the motor today. The gasket has a 3/8" gap "burned" away between 1 & 2 with an obvious hot spot between 2 & 3. The combustion chambers and piston tops for cyls #s 2, 3 and 4 look normal (slight carbon build up with brown exhaust valves). Cyl. #1, however, is clean of any deposits whatsoever (I mean dishwasher clean!), piston top as well. The port side of the #1 intake valve has what appears to be a very fine layer of "speckled" rust or a copper colored substance of some kind sprayed on to it. I see no "obvious" signs of coolant leakage into the port, nor has the car ever experienced an overheat condition. Has anyone else experienced these manifestations or offer an explanation? I fear I may have a cracked intake manifold, however , the port shows no sign of "washing" whatsoever.