I discovered a leak under the tub where the horizontal pipe is attached with the nut to the joint for the drain. Note the "garbage that is stuck to the pipe where the nut/ferrule is joined. When I tried to tighten the nut, the leak got worse. Since there is no clearance/area to move the pipe, it appears I may have to take out the drain pipe from the tub and then reinstall this with a union (if there is room). Any other suggestions would be appreciated. (2 photos attached).