The problem indicated by Bad : modifier in $ ($) is a problem with csh variable syntax. The colon has special significance if it follows a variable name. To isolate it, use {} around the variable name, much like in Perl. So

setenv PERL5LIB ${SOURCE_ROOT}:$PERL5LIB
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should do what you want.

However, the effort you are making to put (parts of) the original include path into $PERL5LIB is unnecessary. What you specify in $PERL5LIB is searched in addition to the original path. So, just

setenv PERL5LIB $SOURCE_ROOT
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should be enough.

Anno