I read somewhere that scuba divers mask sealant can be used on CPAP masks to improve the seal and prevent leaks.  I bought some from an online divers store.  It comes in a tiny jar (at least mine did) and is food grade silicone.  I used it last night and was very pleased.  It puts the Macks silicone method to shame.  The silicone came off my mask with a mask wipe and off my face with soap and water.  It is very sticky.  I went on Amazon and found many products  available.  Also products to use if you have a mustache.

I think this is a great product and should solve most mask leaks.  Of course it cannot make up for an improperly sized mask, but for someone whose pressure needs change during the night I think it's excellant.  The seal you got when you first put on your mask at a lower pressure (Auto and Bilevel)  may not hold when you reach higher pressures- this sealant solves that problem.

Mary