... Trying to solder to a pot body or a trem claw is all but impossible as they act like heat sinks, making the problem even worse. Then you end up holding the iron on the part until it's ruined or damn near so waiting for the iron to heat the part to the point where it'll take solder.
Get a replacement tip with a chisel shape, and life will get a lot easier for you. There are a lotta iron styles out there, but something that looks more like this..Cheers,