Also, when oil filters are not changed at regular intervals, their inner-cartrige may come apart and send bits and pieces of itself into the engine. Not good! So for the $6 you have to spend, you're buying insurance for your engine. I don't know about synthetic, but I have always trusted Castrol GTX 10W-40 in each of my cars.

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Rgds,
Aaron Greenberg
MB technician
'67 250SE Cabriolet
'77 450SL
'79 6.9
'79 6.9
'80 300SD
'81 240D
'85 380SE
'89 420SEL
'93 300E 2.8