If your CVT is only going into safe mode when it's hot outside and when you drive for extended periods of time, and your CVT isn't shuddering, whining,not gearing, et cetera. Then changing your CVT fluid using the OEM fluid would be the best first step to take. Due to the high mileage of your CVT do not change all the fluid. See if you can determine what percentage of the CVT fluid should be changed at 160k miles, e.g, 25%, 50%, 75%, you will want to retain some of the metal shavings to mitigate CVT slippage.
Importantly, you might want to consider just having a Nissan dealership change the CVT fluid to ensure that everything is done correctly, and so you have documentation of the fluid change. If your CVT continues to go into safe mode after changing the fluid, your CVT will need to be replaced. But you're better off buying a "new" car due to vehicle age, and mileage. However, on the positive note, 160k miles on an '08 CVT is a quite impressive.
Also, it's understandable why the dealer never recommended that you change your CVT fluid due to the history of CVT's on '08-'10 Nissans.