My W108 doesn't have that line, but I rebuilt the hose for my pump to box high pressure hose. The fittings look similar so I assume the procedure is the same. Here is the write up from when I did mine years ago. No issues and I drive here daily.
Fixing leaking PS hose
I recently pulled my engine and thought I would document some of the repairs I have completed that I couldn't find in the forum. My power steering hose was leaking and as usual, the local BENZ dealer only had blank stares for me. I did a little research and determined the hoses on my care...