Recentish Text::CSV (and Text::CSV_XS) can deal with separation wider than a single character:

use 5.18.2;
use Text::CSV; 
use Data::Peek;

my $csv = Text::CSV->new ({ sep  => ", ", quote => "'", auto_diag => 1
+ });

while (my $row = $csv->getline (*DATA)) {
    DDumper $row;
    }

__DATA__
(101, '1997-02-25', 'S1', 31.00, NULL, 0.00, 'this becomes two fields,
+ so no go', 5.11),
(102, '1998-03-26', 'S1', 31.00, NULL, 0.00, 'this will remain one fie
+ld', 6.11),
[download]

perl test.pl
[   '(101',
    '1997-02-25',
    'S1',
    '31.00',
    'NULL',
    '0.00',
    'this becomes two fields, so no go',
    '5.11),'
    ]
[   '(102',
    '1998-03-26',
    'S1',
    '31.00',
    'NULL',
    '0.00',
    'this will remain one field',
    '6.11),'
    ]
[download]

But as you want to strip leading ( and trailing ) I think the suggested use of SQL::Statement is fine!

As a side note, newer Text::CSV and Text::CSV_XS can put the while file into the @AoA in one single statement with a filter to clean up the parens:

use Text::CSV qw( csv ); 
use Data::Peek;

my $aoa = csv (in => *DATA, sep => ", ", quo => "'",
    on_in => sub { $_[1][0] =~ s/^\(//; $_[1][-1] =~ s/\),?\s*$//; });

DDumper $aoa;
[download]

[
    [   101,
        '1997-02-25',
        'S1',
        '31.00',
        'NULL',
        '0.00',
        'this becomes two fields, so no go',
        '5.11'
        ],
    [   102,
        '1998-03-26',
        'S1',
        '31.00',
        'NULL',
        '0.00',
        'this will remain one field',
        '6.11'
        ]
    ]
[download]