the previous owner of my s60 t5 used PYB, and when i had to take the pan off at 60k for unrelated problems and it was very tidy (varnish.. doesn't really count) and this was with 5k intervals.
I use GC in my s60 now, but yours is a non-turbo so it is not so demanding of the oil. Just pick one(whether dino or synthetic) and stick with the regiment of changing it every 5k(7.5k w/ syn) miles/6 months.
Originally Posted By: iunderpressure
My 96 850 turbo was ran until 185,000 miles on castrol GTX. After looking into the oil fill cap, I noticed everything was covered with lots of varnish and gunk under the cap and in the dip stick hole. I had a good UOA on GTX HM, a better on Lucas synthetic 5w40 (sheared to 30wt in 5000 miles), but now I'm using Redline 5w30. I'm just trying to clean things up and think it is better in the high temps.
varnish is going to happen with a dino, so long as there is no sludge, i'm not sure you can really blame it on the oil. The reason the gunk was there is because the PCV valve/flame trap needed to be serviced somewhere in the earlier 120k-ish mile range.