Back Reference in Find & Replace

I am trying to use back reference as the help docs state:<br/>
"Back references should have $n but not \n format (as in java.util.regex). "
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Text to Find: &lt;a name="l[0-9]+?"&gt;<br/>
Replace with: &lt;a name="l$n" /&gt;
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I get the error:<br/>
"You have entered malformed replacement string"
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I have also tried every variant of the perl 5/java.util.regex "back reference" to no avail.
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Any ideas?<br/>
I'm using 6.0.4 build#6148