My current mask suddenly started blowing air down onto what would be my mustache if I had one, and on closer examination I discovered that there was a hole at the top of the hose where it connects to the plastic frame that holds the pillow. The hole happened from stress and movement back and forth where the tube connects to the plastic frame part. It was big enough to slide a regular pencil or pen into it.
I tried poking the tube up into the plastic frame part far enough to cover the hole, hoping to glue it in once I got it secure, but it was hopeless. After sitting and staring at the hose with a hole in it for a while it dawned on me that what I needed was a tube of a diameter slightly less than the hose and the plastic frame that holds the pillows, about 1.5cm (0.4"), and after rummaging around a bit I found one. It was a ChapStick lip balm, made in the US by Robins Company, Richmond, Virginia 23220. Mine was almost used up, so I decided to sacrifice the remainder, figuring that my night-time breathing was more important than the health of my lips. I cleaned it out and cut off the ends to leave me a clear tube, and after sticking one end into the tube and the other end into the plastic frame, my mask functions without leaks as before.
If you're an Airfit P10 user who likes to avoid unnecessary expenses, I hope this tip can save you having to order a whole new mask.