A capacitor should have a flat, clean top. And entirely corrosion/leak free. Watch for discarge where they meet the board, too. My experience… It doesn’t have to leak to pose a problem. I’ve saved boards by replacing a capacitor with a bulging  top. www.mouser.com for parts, no minimum. Spring for the UPS shipping. They get crushed in a soft pack by the USPS. 

Good article on Capacitor Selection Criteria

BadCaps.net is another source for information, how-to and to buy capacitors, no minimum