I have a little Etsy store for gameboy repair (though it's currently just carts at the moment), and I had a Pokémon Crystal come in. It didn't load at all and I found corrosion around the cart pins.
Carefully scratching away the solder had it loading up again, but the far right contact (the ground) had solder under the gold finger and I was worried it'll eventually fall away. Originally I wanted to swap all the parts to a new PCB, but that requires actually purchasing another Pokémon Crystal (which sell for around £20-30) - which didn't make sense.
Ultimately I cleaned as much as I could under the pad and then used solder mask to secure the gold finger down and now it's secure and safe for a good many years of usage. Returned to a very happy customer :)