I use Castrol GTX 10W-40 year round in all of my cars with no problems. I just changed the oil and filter in my 300SD a few days ago. The oil change before this most recent one left me stuck using Castrol RX 15W-40 which was ok, but I definitely feel that my cars run cooler and start easier with 10W-40 in them. We use QS 15W-40 at the shop all year, but if it were up to me, I would go for 10-40. Anyways, my $0.02


------------------
Rgds,
Aaron Greenberg
MB technician
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'77 450SL
'79 6.9 (SOLD)
'80 300SD
'85 380SE
'89 420SEL
'93 300E 2.8