Selling it for $300 and eating a $400 loss plus two weekends of your time is not the disaster you're making it out to be. That's the cost of a lesson, and most guys in this trade have paid way more for way dumber mistakes. The real question is whether that feeder will ever work on 12 foot stock, and jamming past 5 feet says the pusher geometry is fighting the length, which is not a small tweak, that's a design problem. You could sink another month into this and still be right here. What's your shop rate? If you bill even $60 an hour, one more weekend of fiddling already costs more than the difference between selling it and keeping it. Cut bait, list it for $400 and take the first decent offer.