problem with soldering rooster esc

[SuperDutyScaler]

my solder gun is a 45W and trust me i can solder, i solder copper ever day at work. ive done plenty of wireing on my r/c trucks over the years but i have neverdone it on the esc itself before. i tried again earlier today and i still cant melt it off the rooster? i have my solder sponge to keep it clean, i tinned the end and tried nothing works on that dam Novak factory solder! what if i took off the heat sink first? would that hurtanything? or will it burn my ESC up?