FYI E36's use ATF tranny fluid in their manual cars.
80w90 will still work (better IMO) but in the winter it'll be stiff to shift till it warms up a bit (uses little over 2L). I also have 80w90 in my tranny already is it eases any concern.
5W50 sythetic is great oil, I pearsonaly use 20W50 synthetic year round, A BMW 4 pot isn't picky about what you put in it's oil pan.
+1 to BigD's post.
"They say ignorance is bliss..... I don't know what the Fu*k that means but I'm pretty happy". Ricky Trailer Park Boys.
Current Mods....X-Brace, Stromung Cat Back Exhaust, 17/225/45 M3 Replicas, HotBits Adjustable Coil Overs, 40% LSD 3:91 Diff, E30 Gearbox, Boosted.