(1) Where any firm is liable to pay any tax, fee or other amount under this Act, the firm and each of the partners of the firm shall be jointly and severally liable for such payment.

(2) Where a partner of a firm liable to pay any tax, fee or other amount under this Act retires, he shall, notwithstanding any contract to the contrary, be liable to pay the tax, fee or other amount remaining unpaid at the time of his retirement and any tax, fee or other amount due up to the date of retirement, though unassessed.