Hello Bassman,

While it's true that regular maintenance, including changing the transmission oil, is essential for the longevity of your vehicle, there isn't a hard and fast rule about never changing the oil past a certain mileage without having done so earlier. The 60k recommendation is a general guideline suggested by manufacturers to ensure optimal performance and longevity of the transmission. However, if you've missed that interval, it's still advisable to change the transmission oil to prevent potential damage and maintain the health of your vehicle.

Changing the transmission oil at 90k miles would still be beneficial and shouldn't cause additional harm to your vehicle. In fact, neglecting to change the oil could potentially lead to more significant issues down the line. It's always best to consult with a trusted mechanic or refer to your vehicle's owner's manual for specific maintenance recommendations tailored to your make and model.