The 924S is a whole different kettle of fish from a 924. The 924S was based off of the 944, and used the 944 engine/transmission. It's not as reliable, and it costs a whole lot more to maintain. The engine is much more expensive to work on, and requires much more attention.
If you want a 924, get an original series, 80-82 with the Audi 5 speed transmission. You'll never let it go