cant find coolant leak after 4 test
 

01 buick lesabre. 97,000.
We did a rad. pressure test, cold, hot and over night, no leak. Also did a combustion leak test, it tested OK. I do have a oil leak at the lower intake . What are the chances that the coolant leak is at the lower intake, leaking a little inside engine? At the coolant resovior i see it drop 1/4" every 200 miles. this happened the last three time it drove it.