Forwarding emails more often than not breaks emails in multiple ways. Think of it like a fax of a fax, it just degrades with every resend.
Here's the code I've been using that seems to work really well when I'm only using one background in an email. If there are multiple background images for different sections I have some slightly different code for that. Hope this helps. It looks pretty similar to yours with a few differences in the styling.
<!--[if gte mso 9]>
<v:rect xmlns:v="urn:schemas-microsoft-com:vml" fill="true" stroke="false" style="width:640px;">
<v:fill type="tile" src="https://santanderconsumerusa.box.com/shared/static/d4t3nvv60uhdirs1aztsq4rh1u4bolbo.png" color="#3b464e" />
<v:textbox style="mso-fit-shape-to-text:true" inset="0,0,0,0">