I did not mean to imply that this could ONLY be a fuel problem, just that the symptoms match well.

Certainly could be the relay.
You can jump terminals 7 & 8 at the relay connector, then feel the pump(s) to see if they operate.

The difficulty is that you would need to catch it in a failure state for this to be meaningful.

Is it starting now, or does it continue to be intermittent?

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1986 300E 5-Speed 240k mi.