MO delivery fans

We have two MO's here, and they have both the same problem with the rear delivery fans. They are on a single speed control dial (one dial for the two fans) but one is about twice as fast at the other. I've tried blowing out the slow one with air and spraying electronic cleaner into them. Nothing helped. Is there a way to take them apart and clean them? Or any other idea how to get them spinning at the same speed would be much appreciated!

 

Chuck,
is it possible that one of the fans have been replaced with a fan thats of different specs?

 

Tom brings up one of only two possibilities...either fan specs have not been adhered to, or a faulty fan. Simple as that.