Unless you are so confident that you've fixed the issues with the MAS, that you are willing to go through all the trouble with draining the fuel and fiddling around with the fuel pump system, I would first get another matching MAS and see what happens. They are not expensive as a good, used, with warranty part. It's also good to have another one for the in-car emergency fix kit anyway, since a bad one will strand you. Remember these parts are over 25 years old now.

For my 90 300E, my MAS went out and my a/c clutch wouldn't engage. Spent $30 for a matching one and all was cold again. It even had a more stable idle!

Good luck.

__________________
03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio