[xsl] What is the correct xpath?

["dvint@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

I have this XML

<test>
   <string key="method">POST</string>
   <array key="header">
        <map>
            <string key="key">Authorization</string>
            <string key="value">Basic  
{{solutionAppID:solutionAppSecret}}</string>
        </map>
        <map>
           <string key="key">Content-Type</string>
           <string 
key="value">application/x-www-form-urlencoded</string>
        </map>
   </array>
  <map key="body">
      <string key="mode">urlencoded</string>
   </map>
</test>

I'm processing the value in <string key="mode">urlencoded</string>. I 
need to marry this with the <string key="value"> in the <map> with 
<string key="key">Content-Type</string>.

I get to the right area with this 
"../array[@key='header']/map/string[@key='key']" I'm stuck on how to now 
match the value "Content-Type" and then find  the content of <string 
key="value">application/x-www-form-urlencoded</string>

So something like this which isn't working
../j:array[@key='header']/j:map/j:string[@key='key']['Content-type']/following-sibling::j:string[@key='value']

This just returns Content-type, what am I doing wrong?

..dan