One of my basses has been having intonation problems lately. For example, I’ll get the open A string and the 12th fret of the A string both perfectly in tune, but frets 1-7 will all be sharp. But I’ve found that if I put a capo on the first fret and get all the strings in tune, then the intonation is good all the way up the neck. Is this an issue with the nut? Do I need to get it filed or possibly just get it replaced?