Does the front brake reservoir in a 2011 Have a plastic disc that fits on the seal before you screw the lid on? Cheers.
Not sure there is on the front one: https://www.officine08.com/p75865_master-cylinder-reservoir-cap-ducati-748-front-brake.html There is a top hat style plastic bit that fits around the inside of the diaphram on the rear ones. Similar to the bit shown in this diagram: https://moto-renzo.biz/Brembo/Brembo-Brake-Fluid-Reservoirs/Cover-15ml.html?language=en those were the first pics I found, so may be a better ones elsewhere.