You need to unscrew the nut and reposition the rubber gasket seal against the sink. The seal is askew and not compressed enough. Sealant is not required.
Ron

There is no way to avoid taking it apart IMHO.

If the picture dictates it correctly, you can see that the drain isn't vertical to the sink and is at an angle causing the gasket to not seat properly. It even looks like a gap is shown on the lower pic. It's not that big a deal to loosen and re-seat the drain. You will want to re-putty or silicone the drain in the sink bowl as well.

I bet the trap below is out of alignment with the sink.

I've done/had the same thing. Take everything apart and start at the top making sure every part is straight and aligned with the next part. You might have to lengthen/shorten a pipe at the bottom to finish correctly.

I would just loosen/lower that nut, swab some pipe thread compound onto it with your finger, then retighten. Make sure to get the compound that's ok for plastic & PVC, etc.