Nate

my daughter's 2001 9-5 Aero with the 2.3t and 135k miles has had quite a bit of trouble with oil pressure problems recently. A little back ground... all oil changes to 30k were the dealer standard synthetic blend and from 30 to 135k it was Mobil 1 pure synthetic.
Around 120 - 125k miles the red oil lite started coming on after longer trips so the car was towed to the Saab dealer in Rockville MD. They said it was an oil return regulator located in the head but accessible through the valve cover. No comments on sludge at that time. The valve was replaced but problem returned so the car was returned to the dealer. They then said it was a sludge issue and after nearly $1,500 the engine was supposedly cleaned.
now at 135k seems to be the same issue. oil lite comes on after fairly short trip, dip stick reads low but if it sets over nite its full and the car starts up no prob, no lite.
so any help here would be great - the car is now in Florida so access to the dealer is tough.
couple of questions
1 - has anyone had problems with this regulator valve? How hard is it to change?
2 - why sludge with pure synthetic? I have always been told this can't happen.

thanks for reading this lengthly post and thanks for any replies !