Have owned a s90 for 3 years now here are some of the problems to look forward to,
1.Radiator is a wear item usally craks at top inlet hose

2.Timming belt must be replaced at 75000 as well as assosiated tensioners and pulleys or you run chance of destroying motor

3.Power seats will fail you must redo cables from motor to fix

4.Engine mounts are another wear item costs are high compared to 240 motor mounts

5.Radio lights will fail replacement costs of bulbs approx. 15.00

6.Front turn signals will melt together on regular basis new bulbs will fix

7.Evap hoses and purge valves will fail giving code po442 and po 455

8.oil separator box will either plug up or develope oil leak

9.Transmissin linkage bushing wiil fail

If you can do work yourself than this is a great smooth running car if not DO NOT BUY