In conventional automatic transmissions, a delay when selecting gears (often reverse) indicates worn internals and the need for a rebuild. Your Nissan is fitted with a CVT transmission rather than a conventional auto, but it still operates on the basis of hydraulic control. Which means that the problem could still be one of internal wear. A transmission specialist is likely to be your best point of contact for this problem.

The first thing to do, though, is check the level of fluid in the transmission. A level that is low can mean delays when selecting gears and even slipping of the transmission under load. However, if the level is low, there must be a leak somewhere as these are sealed systems and should not require regular topping up.

A car that continually breaks the same component time after time probably has a bigger problem than simply the part that keeps breaking. It sounds like you need to have the transmission and torque converter checked for alignment and correct interface. Any problem with the way they fit together could explain why an O-ring keeps failing. Continuing to replace the O-ring won’t fix a more complex problem.

Either that, or the mechanic who is changing the O-rings is making the same mistake over and over again and not using the correct lubrication or fitting procedure.

That's a pretty impressive innings for a Dualis. You obviously maintain it well and drive it sensibly. The engine light on your dashboard is telling you that the car's on-board computer has noticed something isn't right and needs to be fixed or reset. This could be anything from a stretched timing chain to an oxygen sensor in the exhaust system or dozens of things in between.

The best approach is to have the car scanned to see what fault codes the computer throws up. From there, you'll have a much better idea of what the problem is.

The orange or yellow engine light means the car is still safe to drive, but you still need to have it looked at as soon as you can to avoid doing further damage to whatever system is not working properly. If the warning light (of any sort) is red, then you should stop driving as soon as it's safe to pull over and have the vehicle towed to a workshop.