Hello 83MB240D
If the fuel filters have been in for 40K miles; there is little doubt that they need to be replaced.
What calendar time frame does 40K miles translate to?
The valve adjustment can not hurt.
Have them check the O rings on the fuel supply line to the fuel filter housing as a precaution, there is a small possibility that you may be sucking air into the injection pump.
Have you been treating your fuel tank for algae every year?

Averaged 28 mpg; sounds a little low to me for your region.
A fouled fuel tank could be the real issue.
The mechanic can blow backwards through the fuel line, with the filler cap off the tank, and listen for bubbles, if it is plugged up, this may clear enough algae glop to start the car.
Have a great day.

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