Fond several tings that where missing and/or misplaced.
compare your code with mine it works.

my $ff1 = 3;
my @a_ff1;
if ($ff1) {@a_ff1 =  &GetRow("$ff1");};
print @a_ff1,"\n";

   
sub GetRow {
my ($set) = $_[0];

     my $sth = $dbh->prepare("SELECT `filter_partnumber`,`filter_fram`
+,`filter_fleetguard`,`filter_notes` FROM `filter_desc` WHERE `filter_
+id` = ? ") or die $DBI::errstr;
          $sth->execute($set) or die $DBI::errstr;
          my @ary = $sth->fetchrow_array();
          $sth->finish;
       return @ary;
}
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