I have been using a PR DS2 since November (5 months). At my CPAP unit orientation, the therapist indicated that despite a weekly hot-soapy-water wash, the silicone in the mask would get stiffer due to skin oil absorption and would need to be replaced every month or two.
However, I have since bought only a single new mask (because a second mask allows plenty of treatment time for the first mask) because I have been successfully restoring them. Here is my method:
Knowing that montmorillonite clays have an insane adsorption potential due to their high internal surface area, and that this adsorption works well on lipids (think how well kitty litter pulls up oil spills on concrete), I decided to run a test that has been very successful.
We happened to have on hand some finely ground montmorillonite (also known as bentonite) clay powder (this particular jar sold as "Indian healing earth" but I'm sure the brand is irrelevant). I take a mask after it has been washed and dried, and simply put it in a small container with several tablespoons of the clay. I then shake well until all surfaces are coated, and let it sit for a couple of weeks, maybe shaking again if I think of it. That's it.
When I need the treated mask, I first shake out the clay and wash the mask carefully with cold water, then with hot soapy water to ensure all the clay is gone. Then rinse and dry, and it seems as good as new. The silicone is again supple, less translucent, and seals like new.
In the first 2 photos, the mask on the left is the pretreatment version at the end of a month or so of use with weekly cleanings (and was just soaked in hot soapy water for several hours, and then dried prior to the photo). It is getting a bit glossy (especially around the nose cushion) and more transparent, and is NOT sealing well.
The mask on the right just came out of the clay bath, was washed and dried. It is visibly less transparent, it much more supple again, and I expect it to be just fine for tonight's session. The contrast between the two is visible in both the horizontal and vertical photos.
The last photo is my "pretreatment" mask now heading into its long visit at the clay spa. Your results may vary, but I wanted to share what seems to be working for me!