The best way to prevent damage to the Colorimeter is to prevent a spill from happening in the first place. Using lids on the cuvettes is the best way to accomplish this.
There are various models of Vernier Colorimeters. The round model that was sold between 2000-2014 allows you to replace the cuvette holder inside the colorimeter. It can be purchased here: Cuvette Holder, order code CUV-HOLD, $3.
However, other models do not have a replaceable cuvette holder and this may not even fix a corrosion issue. If the colorimeter is still under warranty, feel free to call Vernier Technical Support and we will take a look at it, but it may be beyond repair. Corrosion due to spills is not covered by the warranty. Any attempt to disassemble and reassemble the colorimeter to clean it will void any warranty.