I worked on a friends 47 Plymouth that had several head studs (replaced the bolts on the Alum. head motor) that kept leaking coolant. One of which collected in a spark plug well. Finally removed the offending studs, wrapped them with cotton string on the lower threads, coated the string with Permatex aviation gasket sealer. After reinstall and torquing-leaks were Finally gone. Has been well over a year now, all good.
Head Bolts can and will do the same. Do not jump to the cracked head/block diagnosis just yet. Remove the head bolts adjacent to leak area (spark plug) and try resealing bolts and a re -torque of those bolts and another re-torque of all head bolts when warmed up. Oh ya, you may want to lower the coolant level below the head Before trying this. Saves a mess on the motor/floor! ?
DJ