I think this is not Well form XML . To use xpath in filter to reach exact element/attribute values you can make text as root element like below. However not sure if that is something you can do..
<Filename.log.gz:>
<Message Attribute1="Value1" Attribute2="Value2">
<Message1 Attribute3="Value3" Attribute4="Value4" Attribute5="" Attribute6="Value6" Attribute7="Value7" Attribute8="Value8" Attribute9="Value9" Attribute10="Value10"/>
</Message>
</Filename.log.gz:>
Note: with below xpath any text in root will work fine.
For example xpath : //Message/Message1/@Attribute6 will return Attribute6="Value6"
Let us know if this work for you!
Thanks,
Rajesh k Singh