An 85W-140 sounds pretty thick to me...
Are you sure this is what is called for for your MB? I used the Synthetic Valvolene product in a lighter weight and my shop guy said he felt it was good to go for the life of the car. Also saw a slight mpg increase.
I've been wrong before. But, check the spec?
'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