Benzocaine

Hi I'm trying to install rear konis on my 2001 SLK320 and am having a problem with putting the old parts on the new shocks. Theres a large yellow bumper that slides on the shock first that won't go on because theres a metal button welded on the stem, next is supposed to go the rubber dustcover, but the hole at the top is too small to get past the threads (should I drill it bigger?) There is also a white nylon split washer, is it supposed to replace the large yellow bumper even though it is so much smaller? Thanks for anyones help!