95 E300D Questions about how vacuum relates to start of engine

[Texasgeezer]

On my 95 E300D, 135,000 miles. It's suddenly become consistently hard to start the first time of the day. Takes about 4 tries of fairly long cranking. Then it starts easily the rest of the day.

I've tried parking it pointed downhill on a pretty good slope with a full fuel tank and it is still hard to start in the morning.

I think the most common reason is the fuel drains back and the air has to be pumped out of the lines. But I've tried to eliminate that by using viton o-rings and replacing clear plastic lines with high quality Gates fuel lines and small fuel hose clamps.

When the problem occurred it was immediate. All previous days it would start immediately.

I do not know how the vacuum relates to the fuel shutoff valve.

Does the 95 have a vacuum reservoir or does it need the engine turning to build a vacuum?

Does the ignition switch vacuum valve block the vacuum to the shutoff valve?

Should the vacuum system hold vacuum overnight or does it need to crank to build vacuum?

If I connect a vacuum gauge what should it show before trying to start, while starting, and after shutoff?