Definitely use the post office rather than UPS or FedEx unless specifically requested by your buyer. Declare the parts completely and accurately -- the Customs boys and girls know the difference between chicken salad and chicken ѕhit, so phony declarations of "gift, $9.99" (or whatever) will get the buyer nailed, every time. However, what is required is a declaration of value, not of selling price. Sometimes there is a difference between the two; as long as you declare a real, actual, plausible value for the content of the package, you're on solid ground.