Best month to get the best lease deals?

Lease ending in about 2 months. I currently lease a Mercedes C300 and I am wondering if I should continue with Mercedes or switch to BMW.

I don’t really drive the car and I use it mostly for leisure. I drive probably maximum 3k/yr. I do not use car to commute to work.

I am looking for either 5 series or unicorn 7 series with a 5 series price ;). I could still stick with Mercedes, but what it really matters to me is whether I get a whopping deal or not. Car color, model does not really matter to me.

For the hackers, what is the best month and strategy to go about this type of situation? Should I turn my vehicle in and just wait until December and get a 2019 loaner for a whopping deal? Should I switch to BMW or something equivalent?