Hence, for a seaman to be considered as guilty of desertion, it is essential that there be evidence to prove that if he leaves the ship or vessel in which he had engaged to perform a voyage, he has the clear intention of abandoning his duty and of not returning to the ship or vessel. In the present case, however, petitioners failed to present clear and convincing proof to show that when private respondent jumped ship, he no longer had the intention of returning.  The fact alone that he jumped off the ship where he was stationed, swam to shore and sought medical assistance for the injury he sustained is not a sufficient basis for petitioners to conclude that he had the intention of deserting his post.  Settled is the rule that in termination cases, the burden of proof rests upon the employer to show that the dismissal is for a just and valid cause.[20]  The case of the employer must stand or fall on its own merits and not on the weakness of the employee’s defense.[21]  In the present case, since petitioners failed to discharge their burden of proving that private respondent is guilty of desertion, the Court finds no reason to depart from the conclusion of the Labor Arbiter, NLRC and the CA that private respondent’s dismissal is illegal.   In their second assigned error, petitioners cite Section 19(C) of POEA Memorandum Circular No. 055-96[22] known as the Revised Standard Employment Terms and Conditions Governing the Employment of Filipino Seafarers On Board Ocean-Going Vessels as their alternative basis in terminating the employment of private respondent.  Said Section provides as follows:   Section 19.  REPATRIATION x x x x   C.  If the vessel arrives at a convenient port within a period of three months before the expiration of his contract, the master/ employer may repatriate the seafarer from such port provided that the seafarer shall be paid all his earned wages. In addition, the seafarer shall also be paid his leave pay for the entire contract period plus a termination pay equivalent to one (1) month of his basic pay, provided, however, that this mode of termination may only be exercised by the master/employer if the original contract period of the seafarer is at least ten (10) months; provided, further, that the conditions for this mode of termination shall not apply to dismissal for cause.   The Court is not persuaded. POEA Memorandum Circular No. 055-96 took effect on January 1, 1997 while the contract of employment entered into by and