Why not 'Mae angen eich clust llawdriniaeth'?
That would have to be "Mae eich clust angen llawdrinieath". Remember Welsh is a Verb-subject-object language so the thing doing the verb must come second in the basic sentence structure.
I wrote, "Mae dy glust angen llawdriniaeth." and was marked incorrect. Does that not work the same as your example, but informal? Or, is there something I'm missing?