Chances are very good that one or more of your F10 535i, F06/F12/F13 640i, F02 740i N55 power steering hoses are leaking. Power steering leaks are a not uncommon trait of BMW ownership. Most of the leaks can be traced to old hoses and fittings that have been in service for too long. Just like cooling hoses and belts, rubber power steering lines need periodic replacement. Don't wait too long to replace a leaking power steering line! It's only going to get worse and coat the underside of your engine in dirty oil. Replace them before they fail in order to save you from further headaches and expenses.
This part is manufactured by an aftermarket supplier of European auto parts, including many hoses. While not carrying OEM status, this part follows the design of the original very closely and uses similar materials. An aftermarket part may even have the same TUV approval as its OEM counterpart. The brand may even be OEM to another manufacturer besides BMW. This aftermarket brand has a two year warranty - the same as Genuine BMW and OEM brands.
BMW Fitments:
5 Series
F10 / F11 (11-16) > 535i
6 Series
F12 / F13 (12-18) > 640i
7 Series
F01 / F02 (2009-2015) > 740Li
F01 / F02 (2009-2015) > 740i