1996 Mazda Millenia antifreeze leak

Engine Cooling problem
1996 Mazda Millenia 6 cyl Front Wheel Drive

i just finished with a repair of the knock sensor down in the valley under the intake manifold, put every thing back together and now there is a leak in one of the pipes down in the valley cant tell witch one because the IM is in the way what could be the cause of the leak it wasnt leaking before i started. put every thing back in its place and now the leak do you have to replace the O rings on the pipes every time you disconnect the pipes if not what could i have done wrong because all the rings and gaskets are in great condition please help me i have been working on this car for 3 days now with 8" of snow on the ground with temps in the upper 20sF any help would be great i uploaded a few pictures where the pipes are located to help you understand where i am talking about