It’s possible that the hydraulic pipe is starting to split where it bends at the pivot point on the roof arm, if you carefully part the protective sheathing at that point and look at the hose you should be able to see any damage, if it is damaged then it will either require a new loom (if that’s the correct term) or you could try getting a couple of couplings and a new piece of hydraulic line and splice it in, try a search for hydraulic roof pipe repair
Link to replacing hydraulic lines
https://z4-forum.com/forum/viewtopic.php?f=46&t=122363&p=1748960&hilit=Hydraulic+roof+line+repair#p1748960
Link to repairing
https://z4-forum.com/forum/viewtopic.php?f=45&t=126427&p=1809696&hilit=Hydraulic+line+repair#p1809696