Don't push your luck if the domain has only 1 buyer that is doing business on the name. If they have a trademark, they can file a UDRP against you. Even without a trademark, they're likely to resent you.
I get what you're sayin, but...
1051 sucks so much as a brand, it isn't worth trademark or UDRP fees.
If you wanna be as safe and pure as possible, delete it.