I'm not sure if you've solved it yet, but GmailGuy is correct. You need to convert the body to the Base64 RFC 4648 standard. The jist is you'll need to replace -
with +
and _
with /
.
I've taken your original input and did the replacement: http://hastebin.com/ukanavudaz
And used base64decode.org to decode it, and it was fine.
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