i did a timing chain tensioner replacement a couple months ago without pulling the head/oil pan. i use The Right Stuff gasket sealant, works great. i use a bead on the top of the TC cover, you'll have to cut off the head gasket up to the head and just use gasket sealant. after assembly i smeared some on the joint from the outside as well. dont use an oil pan gasket, use the grey RTV sealant. you shouldnt have to pull the head, but youll have to pull the oil pan if its leaking, replace RTV. if the TC cover is leaking at the head, pull the TC cover again. check your alt connections, make sure theyre all connected, you might have soaked the alt with coolant during TC work, it happens.

hope that helps.