I had no problems sending by USPS to Singapore. It takes about 10 days for a parcel post package to get there.
You should know, however, that shipping from Singapore to the USA is tremendously expensive.
I had a guy who bought a FED-1 from me, then he didn't like the lens which he thought was "loose" when extended. I had no problems, but he was convinced that it should be tight like a vice grip. We then had an argument about shipping costs back to the USA, when I clearly stated in my ebay auction that shipping costs for returns were HIS problem. Eventually he sent it back at his expense. I found out why he was complaining about shipping costs - it was about $45!
So, if you're going to sell to Singapore, make sure you make clear that you are not responsible for return shipping!