diff lube change
The mechanic @ the MB shop wondered why I would "even bother @ ONLY 120K miles..."
I gave him a couple quarts of 100% synthetic 75W-90, he put in a quart and a half, my wife's commuter mileage went up almost a full 1 mpg with no other changes.
He bought another quart and changed the diff lube in his 560SEC and saw an almost identical rise in his mpg.
He now believes...
'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435