use strict;
use warnings;

my $rxTitle = qr
   {(?x)                # Use extended syntax
       (?<=-\s)         # If preceded by hyphen & space
       (                # Open capture
           [^(-]+       # One or more non- opening parentheses
                        #   or hyphens
           (?:          # Non-capture group for quantifier
               [^)]+    # One or more non- closing parentheses
               \)       # Followed by a closing parenthesis
           )?           # Quantify, zero or one of
       )                # Close capture
       (?=\s?</title>)  # If followed by optional space and
                        #   closing title tag
   };

while ( <DATA> )
{
    my ( $text ) = m{$rxTitle};
    print qq{$text\n};
}

__END__
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<title> GRP-124-2 - Alkaline Rust Remover Solution (Ardvark 185L - Rust Remover)</title>
<title> GRP-124-3 - Alkaline Rust Remover Solution (Bee-Dee J84AL - Rust Remover)</title>
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<title> GRP-124-5 - Alkaline Rust Remover Solution (Turk 4181L - Rust Remover)</title>
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<title> GRP-124-7 - Alkaline Rust Remover Solution (Bee-Dee J84A - Rust Remover)</title>
<title> GRP-124-8 - Alkaline Rust Remover Solution (Cadilac HTP-1150 - Rust Remover)</title>
<title> GRP-124-9 - Alkaline Rust Remover Solution (Cadilac HTP-1150L - Rust Remover)</title>
<title> GRP-124-10 - Alkaline Rust Remover (Titanium Long Soak)</title>