Hi buddy, I have used Goof Off on a couple of builds and mostly on my Blue Flame top Tele which had a few stubborn ones where I ended up using a wire brush.

BIG CAUTION - wire brushing can dig deeper grooves than you realise and best to keep persisting with multiple applications of Goof Off. It has an almost Acetone smell and dissolves the blue rubber gloves after a while so best not to get the stuff on your bare skin and reckon it might even melt away your top coats around the area you are trying to fix.

Under GOTM I suggested a thin black line on decal transfer paper and thinking more about it using a dark blue as close to the stain colour might work better on transfer paper. Downside is that it would require a few more clear top coats to hide the edges of the decal transfer.