The black mark you are talking about looks like marker to me. it is common to see boards with marker on them from the factory. as for why the stick is drifting it is because the resistive layer in the potientiometers has worn and causing it to read incorrectly. to fix it you need to [link|https://www.amazon.com/SOSS-GAMING-Genuine-Analog-Joysticks/dp/B087LSGK3F/ref=sr_1_5?crid=1P5FD1XLXQUND&keywords=xbox+controller+replacement+joystick&qid=1681257008&sprefix=xbox+controller+rep%2Caps%2C141&sr=8-5|buy replacement sticks|new_window=true] unsolder the faulty ones, and resolder in the new ones.