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Maybe you've got dry paint build up deep in the ferrule.
That sounds quite extreme. I guess the glue doesn't set because there is no plastic to activate it, so to speak.
Work some acrylic thinners or paint stripper into it, work the base of the brush hairs with your thumb nail to loosen any dried paint, rinse off then work some hair conditioner into the hairs for a minute then rinse off.
I've got one of the GW brushes with the orange tip which I suggest wasn't the best brush in the first place. I was given that one and it had already been used.
The GW brush is one that I'm happy to experiment with. I think that brush soap will be on my xmas list.