Aluminum works pretty well. I have a line-set that has copper bonded to the Aluminum tubes, on both ends.
Copper can be flared and used with MS type connectors.
Is it still leaking out? If it is, you might want to close both of the service valves,
and pull out the power disconnect. (So it can Not get power, while the line-set is cut off from the outdoor unit).
Clockwise with the hex key is off.. They will need a few turns to the stop..