If they can’t flush it, they won’t touch it. I wouldn’t trust a lube tech on that job. I have tried to get the powers at be at my shop to include this on PM services and that went nowhere.The dealer we bought our Sport from does free oil changes so I asked about servicing the PTU just because of that reason. Of course he said that's not something they do...
I have had the fluid changed twice by a good friend who is a Certified Tech, and I have recently picked up the extraction pump (no drain plug) that I need to do it myself. I bought more fluid today and plan to do it again soon.