It is normal for the water pump to weep a small amount of coolant from the weep hole (black stain at weep passage). Do not replace the water pump if this condition exists. Replace the water pump if a heavy deposit or a steady flow of engine coolant is evident on side of the cylinder block from the weep hole passage (shaft seal failure). Be sure to perform a thorough analysis before replacing water pump.
The procedure for replacing the water pump is quite extensive and should be left to a qualified technician. For your own knowledge, here are the steps for removal.
WARNING: DO NOT REMOVE PRESSURE CAP WITH THE SYSTEM HOT AND PRESSURIZED. SERIOUS BURNS FROM COOLANT CAN RESULT.
Disconnect negative battery cable.
NOTE: The water pump is driven by the primary timing chain. Remove upper intake manifold. Remove cylinder head covers, crankshaft vibration damper, and timing chain cover. CAUTION: When aligning timing marks, always rotate engine by turning the crankshaft. Failure to do so will result in valve and/or piston damage.
Align crankshaft sprocket timing mark to mark on oil pump housing. The mark on oil pump housing is 60° ATDC of #1 cylinder. CAUTION: When the timing chain is removed and the cylinder heads are still installed, DO NOT rotate the camshafts or crankshaft without first locating the proper crankshaft position. Failure to do so will result in valve and/or piston damage.
Remove power steering pump and bracket as an assembly. Do not disconnect power steering lines from pump. Reposition pump and support with suitable retaining strap. Remove primary timing chain tensioner retainer cap and tensioner from right cylinder head. Disconnect and remove camshaft position sensor from left cylinder head. Remove timing chain guide access plugs from cylinder heads. NOTE: When camshaft sprocket bolts are removed, the camshafts will rotate in a clockwise direction.
Starting with the right camshaft sprocket, remove the sprocket attaching bolts. Remove camshaft damper (if equipped) and sprocket. Remove left side camshaft sprocket attaching bolts and remove sprocket. Remove lower chain guide and tensioner arm. Remove the primary timing chain. For removal of crankshaft sprocket, Remove the timing chain cover, timing chain, and all chain guides. Remove bolts attaching water pump to block. Remove water pump and gasket.