Product review (5 stars): Just what we needed
I'm writing this without specific knowledge of how this whole process works.  What I can tell you is that my husband wanted to repair/replace some parts for our Aprilaire humidifier (which is about 13 years old).  I ordered the maintenance kit and the replacement solenoid so he could do the work.  He had done some internet snooping to find these two items, but we found the pricing was by far much better buying thru Amazon.  I asked him if he got what he needed with each piece and he said it was perfect.  Everything he needed to make the repair was provided and he was extremely happy with the results and the price.