Tex, that part on the die, inside the 8, is a tip, so it can't fill with grease, that's all. It cracked off.
Tex, If it were a grease-filled die, the digit itself, would appear to be missing. That is because grease and debris would become compacted in the recess of the die which forms the raised number. The center of a number or letter is formed by a post on the die. When this breaks off, metal is allowed to flow into the void. Chris