Not related to this reuse-not-to-reuse debate, but maybe helpful for the OP: I struggled a lot with the oil lines on my motorcycle where I fitted a pressure gauge with banjos. I tried copper and aluminum flat washers, but they all leaked, because the pressure is high at those lines and the thread at the banjo bolt didn`t withstand high torque. So I found these aluminum crush washers with a rubber insert and they worked perfectly. It creates a very good seal even when tightened to a low torque. Newer Japanese bikes use it for brake lines. For example:
https://www.ebay.com/itm/Oil-Drain-Plug-Metal-Rubber-MR21-Crush-Seal-Washer-Set-of-10-for-Toyota-Lexus/273351435154?hash=item3fa503e392:g:LmkAAOSwSixbRtm 6
Definitely not reusable.
Boxster
Threaded Mode
