Another member posted a restoration he is doing on his dads old duster. I spied what looks like a GM washer fluid bottle and mounting bracket circa 1960 to 1969 on the inner fender. I must say it looks pretty factory there. The pix of the bottle and bracket i got are repops from classic industries. The bottle was about $9. Bracket about $8. Cap could be sourced locally in the "help" section of your auto parts store.