Hello, I have a 2015 lancer es CVT with just under 90k miles. I bought the car with 38k miles and had my transmission fluid changed around 58-60k. Up until a few weeks ago, I planned on changing my fluid again but I talked about it with my brother in-law (who is a part-time mechanic) and he told me not to even touch it and just leave the old fluid in it until it dies because changing the fluid will cause the seals inside the transmission to wear down and the transmission will die faster. Is this true? I trust him but I kind of want a second opinion. I've heard that these CVTs tend to fail between 100-150k miles and I just want to do whatever I can to avoid it. I can't afford transmission problems right now :/

Transmission works just fine while driving, it doesn't slip or anything but I live in a very hilly area and do a lot of driving. If anything I have recently noticed a slight delay when shifting into drive and reverse, but I'm pretty sure it's normal.