Tubeless tire became leaky I've been riding my MTB tubeless for the past year without any issue, but for the past couple of days I've noticed that the tire deflates heavily once on a ride. I can't give you exact measurements, but I ride with 2 bars when I leave home and when I'm back home it's probably around 1 bar. It's so bad that I feel the tire 'swimming' when I corner/jump.
I've readded tubeless fluid and tightened the valve nut (I noticed some fluid leaking there), to no avail. I didn't notice any damage on the wheel or the outside of the tire.
What could be the reason that a tire becomes leaky over time? The tire is quite old (~2 years) and also not tubeless-ready (it's a Nobby Nic), but I never had issues with it for the many months I ran it tubeless. Could it be that the tire is just 'too old'?
It could be anything. Submerging the wheel in water will be useful. You might need a new valve, new rim tape or a new tyre. The air may be leaking around the spokes, around the valve, through a hole that is not properly sealed or just through the tyre material (least likely).
Be aware that a hole that is not properly sealed might be leaking air only during the ride when the tyre material is being deformed.
I do not thing you can get a definite answer without testing the real physical wheel.