I can completely understand the feeling of wanting to give up with it - but often I find it's modifying/adjusting/fixing a bass which makes you feel closer to it in the end, and once sorted it will all be a distant memory. Try and forget about it for a week and come back to it fresh when you see Jon. At least he's agreed to have a look, it would be much worse if it was a custom from abroad and you face the endless 'dunno if I can sort that' sort of comment from so called repairers you might get in contact with (most of whom are qualified for no more than a re-string)