I had the same problem on my 96 Mystique. I couldn't find the source. I had it pressure tested and it took over night for it to show. Mechanic said to put some stop leak in because it didn't seem to be in the cylinders or anywhere else that was odvious. Anyways I put 2 cans in and the leak seems to have subsided. At least for the last 10000km's or so.
