Coolant Leak @ Idler Pulley Support ***'ly?

[RWWinslow]

I appear to have a coolant leak developing where the idler pulley support ***'ly bolts to the front of the engine block. Anti-freeze seeps out when the engine is cold, but not when the block heater is plugged in or the engine is running at temperature. Does anyone know if this assly uses an O-ring or gasket material for sealing the ***'ly to the front of the block?