xpath predicate help

I am transforming SGML to XML.
The sample sgml is:

<graphic id="123" name="graphic" ......>
	<grphprim id="456" ....>
</graphic>
.
.
.
<link linkends="999 456">link text</link>

What I am trying to do is. When I find a link to a <grphprim element in sgml
I want the xml link I create to link to the parent <graphic.  The linkends attribute needs
to be manipulated to get the part after the space.

The xml I am using  that does not work 

<xsl:element name="link">
	<xsl:attribute name="linkend">
		<xsl:variable name="link-target"
			<xsl:value-of select="substring-after(./@linkends,' ')"/>
		</xsl:variable>
		<xsl:choose>	
			<xsl:when test="name(//*[@id=$link-target])='grphprim'">
				<xsl:variable name="parent_graphic" select="//graphic[grphprim/@id=$link-target]"/>
				<xsl:value-of select="$parent_graphic/@id">
			</xsl:when>
			<xsl:otherwise>
				<xsl:value-of select="$link-target"/>
			</xsl:othewise>
		</xsl:choose>
	</xsl:attribute>
</xsl:element>

This however does work.  If I hard-code the id in below it works, If I use a variable as in above it does not work. 
Any help would be appreciated.

<xsl:element name="link">
	<xsl:attribute name="linkend">
		<xsl:variable name="link-target"
			<xsl:value-of select="substring-after(./@linkends,' ')"/>
		</xsl:variable>
		<xsl:choose>	
			<xsl:when test="name(//*[@id=$link-target])='grphprim'">
				<xsl:variable name="parent_graphic" select="//graphic[grphprim/@id='456']"/>
				<xsl:value-of select="$parent_graphic/@id">
			</xsl:when>
			<xsl:otherwise>
				<xsl:value-of select="$link-target"/>
			</xsl:othewise>
		</xsl:choose>
	</xsl:attribute>
</xsl:element>