I could probably print you an extruder over the weekend but I'm not sure it'd be neccisary. I've had similar issues with my printer, especialy with 3mm vs 2.85mm fillament. The solution that works best for me is to crank the heat up. I run "large" PLA at about 230. It gets stringy but a quick brush with a torch cleans it up pretty nice. However, I usualy print for fit and function, not usualy for asthetics.. If you need, or want, a new extruder let me know and I'll try to find time on my printer.