As long as the sprocket and washer splines cutouts match / slide onto that of the gearbox shaft, then all that is further needed, is a big hammer, a file and the sprocket lock nut.
1st flatten the washer if deformed. An easy test. Place the washer on a hard flat surface. Place the lock nut on top of the washer. If you are able to rock the lock nut while pressing the nut to the washer surface, the washer is deformed.
2nd a file to trim the outer edge of the washer to allow for proper fit in the sprocket recess. Take care that there is sufficient material left to be able to fold onto the lock nut to allow for locking the sprocket nut in place.
When all else fails, the easy way out is to buy a new sprocket washer. Do remember to take the sprocket with to the dealer, to check for fit.