Thank you, DGP. I'd not considered rocking the transmission. It makes a lot of sense, as it can be at any random angle when checking. The instructor may have gone over that in the initial training for the 206, but I don't think so. Thanks to the contributors above, I won't attempt to add any oil to the transmission unless I just can't get any to show in the sight glass, when hot, and while rocking if necessary. Based on five years with it, I don't expect to.
That's great advice about the hose, too. I'm going to see whether I can procure replacement parts (to give to the A&P) for that hose. It is pretty old.
Just to put wrap it up, I gather everyone agrees that pushing on the small "button" and turning CCW is the answer I was looking for. I did try pushing, pulling, and turning both ways, but there doesn't seem to be any purchase. It just turns and turns without any loosening. By the way, I do have the IPB and all the maintenance manuals, and checked there first. There is no special procedure given.