Mine came with a gasket. Just a little thermal paste - don't worry beyond that - its just to help the heat dissipate. I even think there was a little packed of paste.. (Can't remember now) but it takes slightly more than a smudge of goo.
No +5V explains a lot.. since the PCB board does all the thinking and the CPU needs the +5v to think.
Mine had no -5v, no +15v and no -30v
-5v is on the ARII (replaced power regulator)
+15v is on the PCB (replaced power regulator)
-30v is on the PCB - which I thought was not there because of the +15v - BUT - it turned out that I needed to replace the 555 timer chip.. which somehow takes the -15 and +15 and makes +30v.. which then feeds the high score retention chip (which my pcb did not retain high scores)
I just did the 555 last night - but haven't tested the high score yet - monitor was apart on the bench.. but I'm 99% sure it will work.
You look to be in good shape - until the next item down stream is broke - but good digging!!
Now the hard part... waiting