Also, why does old battery gunk have to look like earwax... ๐
White vinegar is better than alcohol for cleaning battery corrosion. Battery acid is actually a base, so the acidic vinegar neutralizes it.
Another thing worth noting is that these things usually have a screw somewhere that adjusts playback speed. Though, it doesn't always look like a screw. You may find that you have to adjust it after you get the new belt.