#1 rule is F&F deals are always shit. Keep your CR-V and start reading the forum. You will learn a lot here. You made the most difficult step by finding the forum before signing something. The rest is easy peasy.
Many mainstream Mercedes models (not including EV’s) have always leased better at 42 and 48 months than 36, which is what the dealer was talking about.
While the RV will be lower at 42 or 48 it may only be slightly lower, so it makes the payment more favorable. (I’m currently towards the end of a 42 mo. MB lease, FYI).
But obviously with a longer term there are other factors besides just the payment like registration, tires, maintenance, etc., so take these into account as well.
But this is where you need to take a step back and do some homework. Get the relevant RV/MF numbers for the GLB and plug these into the LH calculator, play around with different terms and see exactly how each prices out.
This way YOU are making the decision of 36/42/48 and not just doing a 42 because the dealer said it was best.