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'?