The reason that had you resort to pliers nay make removal now impossible.
I'd start by removing from the bike and scrubbing with water, dish detergent and a toothbrush, especially at the slot.
Then dry in a toaster oven at 180 or so g or an hour or so. Finally use penetrating oil.
Try to gently turn it with a Torx key tapped in so it cuts the shape and can drive it. There's a good chance that you'll need to drill it out, then re-tap to clean out the thread.
Overall, if cleaning and penetrating oil doesn't work, the alternatives may be costly enough to suggest shopping for new levers.
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