Amazingly, I have seen "MOD" discounts at a number of Marriott timeshares in recent weeks - many for stays during the busiest weeks of the year. I'm not giving away where I have seen them yet, because I'm still trying to decide whether to rent from Marriott. But if you have tried without success in the past, try again now.
Several of the discounts include the extra 10% discount (total of 35%) for using the Marriott Visa card.