2000 Other Jaguar Models leaking coolant

i have a 2000 jaguar s-type 4.0 v8 it seems to be leaking water some where in the engine. i have taken it to a mechanic and they say it is probably coming from a rubber o ring where the coolant goes in they say it will take a long time to fix because of the location of two bolts that hold it together. however it seems to me like the leak is coming from somewhere else any suggestions