Partner liability: partners are jointly and severally responsible for firm tax, interest and penalties unless retirement notice is given. Where a firm is liable to pay tax, interest or penalty under the Act, the firm and each partner shall be jointly and severally liable. A retiring partner or the firm must intimate the date of retirement to the Commissioner in writing; the retiring partner remains liable for tax, interest or penalty due up to the date of retirement, and if no intimation is received within the prescribed period the partner's liability continues until receipt of notice by the Commissioner.