If your idle temperature is 10-15c. over ambient, your cooler is likely ok.
While, in time paste can lose effectiveness, I would not dissemble a aio unless I had a good reason to.
Many things can go wrong.
Install a monitor like HWmonitor.
It will keep track of your minimum, average, max temperatures.
I would not worry about 90c. spikes.
Your processor will throttle or shut down if it senses a dangerous temperature.
That is around 100c.
Since the pump is a mechanical device, in time it will fail.
If you are having doubts about your unit and want to replace it, I would also recommend a good air cooler.
It will be quieter and cool equally well.
If you have 160mm height available, I recommend the noctua NH-D15s.