The standard party line is Mobil One 0W-40, but I have never used it.
http://www.renntech.org/forums/index.php?showtopic=9454&hl=unapproved
Neat trick on the T50. Don't know anyone who uses it because everyone uses an 8mm allen. Was playing around with a spare drain plug one day and much to my suprise a T50 was a perfect fit. Showed it to the mechanics at the local dealer, as they also use a 8mm allen. Might be a help if the recess for the aluminum drain plug is rounded and an 8mm slips.
For those without metric tools a 5/6 inch allen is about as good a fit as 8mm.