Generally speaking you should not store distilled spirits on their sides for long periods of time, the high alcohol content can break down the cork and transfer cork flavors back into the spirit.

If you are having trouble with some particular corks, I would suggest replacing them with some higher quality t-corks from your local liquor store or online (lots of stores have them, google away).

My scotch doesn't usually stick around long enough to warrant me using these, but I do use them for bottles of absinthe and they work nicely.