I've heard many others complain about the flint screw issue. It's not your fault, it's a design flaw. I've heard some people put a bit of Loctite on the threads, and that will keep it in place. Don't purchase the "permanent" type -- get the blue "removable" type. http://www.loctiteproducts.com/p/10/15/t_lkr_blue/overview/Loctite-Threadlocker-Blue-242.htm You'll be able to break the seal when you need to change the flint, but just a drop of that stuff should help to keep it from backing out. Also, don't worry about accumulation on the threads -- it's basically sugar water, so you can just clean it off with an old toothbrush and water or alcohol if you so desire.
As for the fuel tank issue, did you bleed the tank before refilling? If you don't bleed the tank each time, air slowly accumulates in the tank, which means less fuel can be added to the lighter. As this air bubble grows inside your tank, the capacity gets less and less. So even if you sit there for ten minutes with the butane refill pushed into your lighter, only so much butane can actually be transferred to the lighter. You can bleed the tank with a clean, small screwdriver or other similar object. Just make sure it is clean and not too sharp. Debris can be transferred to the tank during filling (which is bad), and if you use a sharp object, you could damage the fill valve, which is obviously bad as well.