If you are talking about the washer between the caliper bracket and the axle shoulder, its not a big deal.
Only thing you need to watch out for is that you don't run out of threads while tightening the axle nut. As long as there is enough threads there to torque the nut, that washer can be eliminated.
Its only purpose is to keep the caliper bracket from getting jammed on the axle shoulder.
I removed mine to gain some thread length since I have a PCW shock relocation bracket.
Regardless, I'd be trying to find the washer. :biglaugh: