Is it no longer sticky because bits are stuck in it? I'm sure people have previously suggested getting some strong new aplix and repeatedly applying it to the old stuff to pull the bits out, if that makes sense.
I revive mine by using the cats slicker brush. You can get a cheep slicker brush from wilkos. Its the one with all the wires on that are bent at an angle. then just brush the aplix with it. It gets rid of most of the stuff that sticks in it