I am in need to send an engine for repairs to Japan.
Wanted to know if anyone has sent anything abroad for repairs and returns and the process for the same.
From what I could read up (in public domain) one needs import document and you are taxed twice while exporting out and importing? I bought this engine second hand and have no documents for when it was imported by the original buyer
May be some one has sent thier radio etc to Futuba for repairs and would know how to go about it.

I must confess if you want to import (for perosnal use through post) ,I can tell you almost all that is required but I am at sea with the above query   

Any help would be appreciated

Gaurav Agarval (gauravag) seems to have sent a radio to the US for warranty repairs. 

http://www.rcindia.org/radios-and-receivers/futaba-10c-trim-tab-problem/msg19847/#msg19847

You can send if the Engine is costly one, Else buying a new Engine is good suggestion considering the to and fro  shipping costs(Since you said it was old one and as it have no warranty.).