ive seen it many times where the vent baffle droops a little and contacts the float when you try and set it to the correct level.

try setting the float about 1/2-3/4 of a turn lower than the "correct" height to see if it eliminates the flooding condition you're having.
if this fixes the problem, you need to tweek the vent baffle upwards a bit.
i find that shortening the baffle can help in this situation as well.

ive also found that the nitrophyl or brass floats are less likely to experience this issue than the plastic floats(which have much more flexible arms).

if that doesnt do it, then it really either has to be a needle and seat, or needle and seat o-ring, or the regulator is malfuctioning.
if the regulator is old, the diaphragm may be dried out and stiff.