There was some kind of gunk / dust deposit on my stylus. I couldn’t shift it with brushing. Enter Winyl One-Touch Polymer. Within 30 seconds of dropping the stylus on the Winyl polymer and then lifting it, my AT400ml was back to normal. The offending deposit now sitting on the polymer and not on the stylus. Now happily listening to Buena Vista Social Club. Excellent product. Best 25 quid I’ve spent. Feels like an upgrade!