450c with leaded is too hot, you're burning the flux off almost instantly which is why you're having to add flux. Try a K tip and just continually feed solder while dragging across a row of tht connections. Unless there's a joint connected to a big ground plane, I would solder 350c max with leaded.
450 is way to hot for leaded solder and using a fiberglass pen is overkill on those pins. You can easily solder at 300 to 320c. Soldering at the lowest temp you can get away with is always best practice!
