I had two engines 'Failed to Send" just last two weeks. It's a real pity, I was however fully refunded and the seller kept his funds, but the engines seemed to have disappeared.
The only way to send out from the USA is to ask the seller to post it to you directly and not through the shipping program. I have emailed/contacted sellers to check their procedure and if they ship with the 'global shipping program' i just give it a miss.
Unfortunately ICAO consider (rightly so) internal combustion engines a dangerous good, and there is no size discrimination so a 2.5cc engine is treated like a 351 V8 so to speak, due to the flammable liquids or remnants of trapped in the engine (even if new). SO frustrating.