I have what I think is a 1991 Grohe Metro E shower fixture in my master bath. The valve system recently broke – can’t turn water on, handle just spins. When I took off the handle and removed the cartridge, i found that the “universal” ball joint (controlling flow and temperature) had broken and I guess I need a new cartridge but I can’t find a part number on any item...and no online part site will help w/o it....Suggestions on how to look this item up?

-george