R2-D2 survived a direct shot by Darth Vader during the assault on the first Death Star. (Not sure how somebody as Force powerful and skilled a pilot as Darth Vader could have missed blowing the X-Wing fighter apart instead of merely nicking a mere astromech droid, but hey, we'll go with this.)
R2 comes back all beat up and C-3PO promises to gladly donate some of its circuits.
How much damage did R2 receive during the battle?
Was its "brain" destroyed and many (all?) of its memories zapped?