Something like this (not tested):

use strict;
use File::Basename qw(fileparse);

my %paths;
for my $source (@classedSources){
   my ($file,$path) = fileparse($source);
   push @{$paths{$file}}, $path;
}

print "\n";
print "-" x 80, "\n";
print "-- REPEATED SOURCE(S):\n";
print "-" x 80, "\n";

my @duplicate_paths = grep { scalar @{$paths{$_}} > 1 } keys %paths;
for my $dup (@duplicate_paths){
    print "\n$file" . join("\n      ", @{$paths{$dup}});
}
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