I have the same Problem. The pastic Box seems to block the tonearm from moving freely up and down. Have you managed to solve the issue?

I found this to be helpful as well.  https://www.vintage-radio.net/forum/showthread.php?t=176737 In my case, the mechanism lost the plastic ears on both sides. I used the bent wire idea from the attached thread and held it in place with a match stick beside it in the hole.  This is for the right hand side looking from the back, and allows for operation of the mechanism without fouling on any other parts. For the left hand side one, I used a zip tie. The one I had was 1.5mm wide, and needed to be reduced in width to 1.2mm to fit the hole.  I removed the zipper tongue with a sharp blade.  Then fitted the modified zip tie and used the zipper part from a second tie to secure it so the 2 parts of the mechanism were parallel. The zip tie has advantages - it is flexible so easier to fit through the hole in the mounting plate, and if the zip is overtightened, the zipper part can be cut off using miniature side cutters leaving the styrup part intact for another try. With these 2 fixes, the arm works perfectly again.  Thanks to Martin for his initial inspiration.