This isn't a huge problem for DSLRs since the shutters give out way before the dampener, but if you're like me and you shoot film cameras that are 3 times your age you will come across this issue all the time. They usual deteriorate from age or get torn out by accident.
You can buy replacements online for $12-20 plus shipping, but here is a super simple fix.
Just use the self adhesive window foam seal, I like the 1/8", the 1/16th size one is great for light seals as well. A singe strip ran me $1 at Ace hardware, it had enough to do ten of my 35mm SLRLs.
Found out the hard way what happens if you dont replace this dampener years go when the mirror on my first ever 35mm camera broke into pieces one day.