Having it looked at tomorro,crossing my fingers that its an easy fix that wont cost an arm and a leg but either way better safe than sorry.thanks for the advice will keep you updated on what the mechanic says when i know. 
Good luck! Let us know…
99 deville has coolant recovery tank which has fill cap. U add coolant to this tank. Radiator has no fill port.
My 99 deville (De Elegance) doesnt have recovery tank radiator does have fill port…can you tell me where recovery tank is sapost to be located?we looked everywhere and couldnt find it.
Looks like im wrong,i googled it the one in mine is just like one pictured but it has the radiator cap on it…?im slightly confused
Ok, looks like u found fill cap? Do not overfill tank. It is an expansion tank. There needs to be an air gap at top. If u fill it to top, it will burp out when motor is hot. That may cause more confusion about where ur leak really is.