While I have been working on a sub-panel and run into questions about the wiring there, I finally got around to looking in the main panel. See photos. If I am looking at this right, the main panel was never grounded which is likely why the subpanel had wierd (in my mind) wiring.
There is a ground at the meter, but only one bus, which is isolated (floating?) with all the neutrals and grounds connected there. There is a location on the opposite side of the panel for attaching an "equipment ground" but nothing is attached there.
The house was built in the 1970's. Would it be worth the trouble of:
Running a ground from the grounding rod below the meter to the panel?
Running a single neutral conductor from the subpanel? That panel is wired for 240 and I have two hots and a ground which goes back to the main bus where all the neutrals and grounds are bonded together.