As a followup, I've been trying to eliminate a rough idle problem in my 300SEL. As part of that, I've run a bottle of Techron Fuel System Cleaner and three bottles of Techron Pro-Guard through my gas tank over the last month or so. Two of the three Pro-Guards were on a mostly empty tank. I almost never see the gauge act up anymore.
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino