Aluminum oil drains are OK because they are not stressed during engine
running.  My take on the subject is if an oil hose will flex because one end
is attached to the motor and the other end is attached to a device on the
firewall; flexing will occure due to differential movement thus the aluminum
will work and eventually fail.  That is the reason for steel fittings as I
understand it.

Bob Smiley
N94RJ