I had one badly made M3 washer, it had a flat on the circumference - I still used it. If you are unsure of anything, still build it but then replace the washer when you get replacements.
As for the white rings on gears, they are very tight. Hold them under hot water from the tap to soften them, then put them in position - if too tight to get the final click, turn over and press down on a hard work surface. This is what I did when my thumb started bleeding. Ive since built another car doing this, and no injuries on the second kit
