[DonC]

I agree with Charlie. Just like Nylock nuts, the copper washers should never be reused. Any fastner or gasket (in this case copper washer) that depends on distortion for it's function should only be used once. Any other application of the same element will result in the previous distortion deteriorating the new application by carrying over the form of the previous distortion. The previous distortion will almost never fit the new application correctly.
In the case of the brake line the pressures that the copper washer have to seal against are very high and the seal has to be nearly perfect.
You may or may not get away with re-using something like this but why take things apart any more than absolutely necessary or re-do work you've already done for a couple of cents.
DonC