If it's just the padding I'd suggest using a different glue to hold it in. For the padding to bond to the glue it can't be dried out and crumbling -- in that case you'll need to replace the padding itself (I'm not a goalie so I don't know where you can get replacement padding). If the cage or the mask is cracked or broken you shouldn't even play with it.
I don't know how long a goalie mask typically lasts but one hard shot can crack it. Former Bruins goalie Hannu Toivonen had just gotten a new mask -- defenseman during practice took a wrist shot from the point and cracked it. I don't think the mask was more than 3 days old.
Do you require CSA certification? The mask will last a lifetime as long as you see no cracks. The shell will not become brittle or less protective simply due to age.
Try calling/e-mailing THR in Toronto. Total hockey Repair. they will give you a quote on replacing hte foam padding.
Have you ever checked into the gel interior offered by maltese hockey? the cost is a little more than a complete replacement set of foam pads but its much more protective and easy to install.
The Maltese SPS system will increase periferal vision, increase the level of protection and eliminate the sweat that runs into the eyes. The gel is thinner than padding so will allow a bit more room in hte mask and let your face be closer to the opening, improving over all vision.
Just a side note to go along with a previous poster, if you notice the cagte has bent bars or is the variety with the single bar center cats eye, replace the cage. The single bar running up the middle of the old style cats eyes are prone to break and bend inward towards the eye. That is why newer cats eyes have the double vertical bar. Any bent bar, if you stry to straighten, will become even weaker. IF your going to keep wearing it, leave any bends alone!
For the existing padding you should try hot glue or garrilla glue. Either should work. it is very important to make sure you get all the old glue off the shell. Place shell ONLY(remove hardware) in the freezer for several hours and then use a putty knife to remove the old Hot Glue from the shell.