Well, oil sludge is not a problem with the B204 engines!! It only occurs on the B205 which were in model-year 2000-2002, so chances are, that your car are not affected!!
The Direct Ignition Cassette, is a very well known problem, and SAAB is currently running a campaign in Sweden where SAAB pays for all costs in changing the DI cassette. Contact an authorized dealership and look into, if you can get the costs covered!!
I have been reading a lot of comments from people in regards to GMs involvement with Saab. I continuously see consumers who are uneducated as to the degree of involvement GM actually has in the manufacturing of Saabs.Yes, GM owns them, however they are not a GM, they share mainly the chassis and a few common plastic pieces, sensors and what not, nothing major. They are completely designed and made by Saab AB. There are some undeniable quality issues off and on, but that is true with any manufacturer. Often times a lot of problems consumers have with their cars are due to their own neglect of maintenance, if your going to spend money on a higher end car then you should also be aware that it will require a little more upkeep and attention than your common car. I have been around and owned Saabs for a long time, both old and new, with regular servicing, no serious problems.
Well, fortunately, you don't have to worry about the sludge problem with 99 9-3, It's 00,01,02.
Go to: http://en.wikipedia.org/wiki/Saab_H_engine for a good explanation of the features, differences, and likely cause of the issues with the B205 engine. It seems that's the one, and there is an explanation for it. Unless you are VERY confident of what you are buying (get it inspected by a Saab dealer first I think), I would stay away from that engine - unless it has just been rebuilt at someone else's expense and has a new warranty!