I have been running on 10W-30 Mobile-1 engine oil for a couple of months - It helped my 1-2 shift alot. May try the redline next time. I went with 10W-30 'cause it's what the manual and FSM for my (1980) recommends.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT