What spec is it? I have a Marquis 7000 NHM, Spec D I can send along. Also have a service manual for a Spec J-P (in case you don't know the spec is the last letter in the serial number). And the "generic" Onan service manual. Let me know which (or all) you may be interested in. Unfortunately, knowing your SPEC is a big, darn deal--especially if you go to Cummins for parts.
What are you wanting to do/fix? I'm no 7000 wizard yet but am getting there by necessity. It is possible I may already have run into your issue.
OH, you may also want to check in on:
Onan Generators - SmokStak
The folks over there have been awesome !