Using washers to fill gap between top support component and IKEA IVAR cabinet

I have an IKEA IVAR pine cabinet, the 80x50x83cm version – like the cabinet here.

I have installed it into IKEA IVAR side units, 50x226cm – like the side units here.

Here are the assembly instructions.

The side units are over 15 years old, which may explain the following problem:

There are supports which plug into holes in the uprights and have a protruding part which contacts the cabinet. The supports go on the top and bottom of the cabinet. There is a hole in the protruding part for a machine screw which screws into a hole in the cabinet to steady it. (See pages 16, 17 and 18 in the assembly instructions.)

The cabinet is properly seated on the bottom supports, and screwed in correctly. However, when it is properly seated on the bottom supports, there is a 3mm vertical gap between the protruding part of the top support and the top of the cabinet. The top machine screw is then too short to properly screw into the cabinet.

I phoned IKEA. Their suggestion was to order new uprights. I would like to avoid that.

• Is it a reasonable solution to buy new, longer, machine screws (14mm)
  and use a 3mm stack of washers to fill the gap between the support
  and the cabinet?
• The metal washers which fit the British Standard for an M4 machine
  screw are 0.8 mm in depth. I’ve found nylon washers which are 1mm in
  depth. How should I arrange my washers so they fill up the space
  underneath the support fully? Can I mix washer types? (I’m not sure 3mm is an exact measurement.)

The part numbers in question are:

• 103887 for the supports
• 100404 for the screws

The IKEA parts catalogue, which gives the dimensions of individual parts, is available here:
http://www.icomp.webcms.se/index.cfm