I did a bit a research on EPC and it looks like Some M120 came with a single power steering pump (non-tandem). P/N is 140 466 41 01. They share the pulley with some pumps found on M104s. P/N of these pumps is different but from pictures I saw on the net the difference seem to only be the fluid reservoir on top. So it looks like I could get an M104 power steering pump and swap reservoirs.