Same, I have the same experience. My son, now 2-year old, can stand the bitterness of the "finger-water" and is still sucking his thumb. I started using the "finger-water" when he was only 1 but it was not successful.
My son seems to understand that sucking fingers is not good, and that's why he does not suck it during the day. He only sucks it just before having milk, before falling to sleep, and when he is in deep sleep.
I am running out of ideas to stop him from sucking, I would like to hear from other mum about their successful experience of getting rid of this bad habit for the little kid.