i believe Squadron Putty uses tuolene for a vehicle, which explains why it melts its way into the surrounding styrene to form a bond.
for $3 it may no be worth trying to reconstitute if it has gone hard in the tube. but i have heard of the disolved styrene in MEK trick. again it seems like a lot of work to me [like trying to reinvent the, uh, computer] but is purportedly the best way to insure no shrinkage in the fill. i think it is because there are no dissimilar materials to separate.