Hydrogen is very low permeability in HDPE or aluminum and it embrittles neither of them. Modern carbon fiber tanks are lined with HDPE and aluminum they lose less than 1% per month via seepage the gas lines are also HDPE lined a properly engineered composite H2 tank and feed lines will lose little to permeability or seal leaks. Nasa uses hydrogen on the regular as does every oil refinery in the world in quantities of millions of kg per year. The issues of leakage was solved with composite materials years ago.
NASA, rocket applications, and refineries can all afford expensive seals and the maintenance they require to keep the seals, glands, packing, and gaskets tight. I really doubt those solutions will be cost effective or maintainable by low-skill labor in millions of refueling stations and millions of delivery tankers.