Parker Double Repair question

[RHanlin]

Please forgive me if this has already been addressed in the past "but".... I've got a Parker Double that the locking lug fell out of. It's the piece the forend locks into when re-installed. It appears that this piece was soldered in place but I am having trouble getting solder to flow back even after cleaning all of the surfaces. I'm putting the heat on the same side as the lug but the solder just beads and runs off. I was afraid of applying too much heat but it looks like the beading might be an issue of not enough heat on the area I'm trying to re-solder.

Am I right? Is there a better technique to this repair?

Thanks