In my experience, cleaning the pots will be a short term fix at best. If you're going to go through the trouble of taking the mixer apart to clean the pots, you may as well replace them. There are only 4 on that board, so it won't take much time or expense. As for the take apart goes, I haven't disassembled that model before so I can't be of much help. You might try contacting Mackie/Loud support and see if they can send you a PDF of the service guide.
Greg
Techmail@loudtechinc.com
Parts: Parts.Messaging@loudtechinc.com