Have your clear stamps lost their ability to cling to the acrylic block?
Here is a solution for you:
Coat them with Aleene's TACK-IT Over & Over
Let it dry and voila--Now they will bond again.
This product can be found in the craft section at Walmart.
It is a pressure-sensitive liquid glue for a temporary bond,
so I suggest that you do not get this surface wet
when cleaning your stamp.