Forgive any old vandalism? 

Should we forgive any vandalism if it is old?

At first, I thought the vandalism was just an honest mistake.  If it were, the user would say so.  He nasty to me and denies making the edit even though the diff is clear, he did.

That's why I think the person needs to be blocked so we can check his work.  He might be hiding sneaky vandalism with hundreds of grammatical corrections.