Hello MATTMOG. What a coincidence. Same happened yesterday to my 2019 Plus4 (Traditional) after 41000km. Reservoir looks exactly as yours. Brown scratch where fluid touches the mounting bracket. Intermediate solution with max level tape.
[Linked Image]1000015787 by Werni Wehrli, auf Flickr
[Linked Image]1000015794 by Werni Wehrli, auf Flickr


Plus 4 110 Edition 2019