If you are referring to the threaded part that allows you to use a crank extraction tool, I did the same thing to the left crank arm (too impatient and stupid to check for the washer).

I managed to disassemble the entire bottom bracket and ended up replacing that and buying a new/used Shimano 600 crankset to replace the damaged crank arm. Right now, the latter is still stuck to the BB spindle in a box of spare parts...