As the OP stated, the car has an MAS, no fuel pump relay, but a failing MAS could be producing the same symptoms that Gilly described for a fuel pump relay. Incidentally, if you know that the voltage reg is not charging properly, why not just replace it and remove that from the equation? A regulator is inexpensive and easy to install.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't