Enamel thinners do not play well with acrylics, especially Tamiya. Causes it to gunk up real bad. Triarius would have a multi-syllable technical word for it
, but I'm feeling a bit off today so I'll stick with "gunk". Brake fluid is one way of cleaning it up, but a simpler one might be dumping the whole brush into a tub of Windex with ammonia. The O-rings will be unaffected by it, and it's a whole lot easier to clean up than brake fluid!