Allow me to respond as leader of the SAAB 9-5 Sludge Paranoia Cult. This is all worst case but it's better than riding along blissfully unaware until you see that rod fly through the hood.
Yes, the 9-5 CAN be a sludge prone car. Depending on the year. For the 9-5, 99-03 are the key years while on the 9-3, the 99 Viggen and 2000-2002 all trim levels are ones to wach for. The Aero, however, is LESS sludge prone than the base 2.3l turbo. Still, it would be good to know the car's service history. If anything other than synth was used, I'd be willing to bet that the oil pickup screen is at least partially clogged.
How many miles on this car? There ARE fixes for the problem. Much of the problem stems from an overworked, poorly designed PCV system. SAAB recently released a 6th version of the update kit for this and seems to have finally gotten it right according to independent testing. Steer away from the car if you see smoke on startup, excessive varnish on the dipstick, or any odd, loud engine noises.
Unless the car is high mileage, it's probably not too late to stem the damage. I would take it to a mechanic and have the oil pressure tested, along with dropping the pan to clean the pickup screen AND installing the PCV update kit. The kit is only $50. If you are getting the car at a decent price, it is WELL worth it. The 9-5 AERO is a spectacular car and can be upgraded to make it a real screamer....if that's your thing. There's a poster on here who thinks I am crazy for bringing all this up b/c his personal 9-5 seems okay. However, as a moderator for one of the biggest saab forums on the net, I can tell you PLENTY of folks have had issues. But they aren't that hard to get over and when you do, you have a great car.
As for arx, yes, I used it for two clean cycles and now run it for maint. It cleaned pretty well but unfortunately, deteriorated rubber hose is one of the things that clogs the pickup screen and even arx can't dissolve that.
PLEASE, don't let me scare you away from a great car. But it'd be dishonest for me to tell you everything's fine. Sure, some people sail along troublefree. But some don't....
