You need some rubbing alcohol, a box of q-tips, and a screwdriver. Your controllers will be as good as new. Cleaning your old hardware and software is the price that every retro gamer has to pay to play on the original hardware. It's worth it. And once you beat Ghosts 'n Goblins you can tackle Battletoads.
I just bought Sky Shark, R.C. Pro-Am, and Ironsword: Wizards and Warriors 2 last night. It took me 7 game overs to finally beat the first level in Sky Shark and then I promptly got a game over within a minute. I love NES games.