Welcome to Beoworld.
I have repaired the sliders on BM 901 and BM 2400, as I never found replacements that fit exactly, repairs was mainly, open them, cleaning and glue broken pieces, its a PITA job but doable .
But it could be that they, or similar, are available here, if you find replacements for, or repair, yours, pleace keep us posted. We love pics.
I did my BM 901 like this
Beosound 3000, BL 4000, BL 8000, BG 2404,BG 5000, BG CD50, Beocord 5000, BM 901, BM 2400, BM 4000, BV S45, BV 3702. There is nothing we cannot do, but a lot of things we don't want to do!!