I had a similar issue 2 years ago while I was working on my car. I saw those rubber hoses on my 560sel also rotting, after 20+ years and still being original it was time to replace them. Well, I just used a cheap rubber from pep boys hose and a month later it started to leak again. I ended up going to the dealer and getting the correct host. It is a different material and looks like it expands to a point when needed. I have not had issues since, I would look into using the original hoses from the dealer or even a very good aftermarket replacement
Check the ebay link below, I get something similar from the dealer, just much longer since I didnt know how much I would need
Mercedes W115 W116 W126 Contitech Fuel Expansion Hose 7 0 x 14 5 mm 0009975152 | eBay