Where is the leak? Can you actually see it or are you having to top it up alot? If you cant see a leak check for damp carpets or water in the oil. Don't fill the rad beyond the max level as it will only blow it out when it gets hot.
Sorry I answered your question regarding where the thermostat is but this is unlikely to cause a leak, but would cause high temperature if sticking in shut position.
Mark
December 2005