You mention that it is a 996, and a 98 model... therefore it was one of the first 996 models on the market. Those suffered from some quality issues with cheap internal and external work, some engine failures due to RMS. Trade it in and get a 993.
Yes I agree with the 993 suggestion. Buy one! Anyone who can't see why the 993 is such a fantastic car doesn't understand what a 911 is all about. Yes the 996 is more modern, but it is not anywhere near as special. Porsche are on the right track with the 997 (especially the GT3) but there will never be another 993.
I own a Porsche Carrera 996, and having previously owned a 993 and high end sports versions of both Mercedes and BMW, I feel that I can add to this discussion.
Firstly the Porsche 993 and 996 are a class apart from the Mercs/BMWs. The 911s are designed from day 1 to be true sports cars and have none of the engineering compromises of tuned saloons such as the M3. The Porsches are focused towards a true drivers needs, and do not merely flatter to deceive. Perhaps this is where the comments about jittery brakes come in; the 996 brakes lack servo-assistance in favour of direct pedal to brake hydraulics to maximise feel and feedback. The reason you think they are jittery is because you can actually feel what is happening on the road!
It is perverse to consider the 993 a better car in any way than the 996. The 911 has evolved and improved with each generation while maintaining a consistent philosophy. It is for this reason that the 996 is now replacing the 993 and becoming the track car of choice for amateur Porsche enthusiasts.
Among those I know who own and race Porsches, this obsession with a particular engine cooling method over increased performance and reliability is considered plain bizarre!
I just can't wait to get hold of a 997.