All corks have a parafin coating. The problem is primarily two-fold, age of the cork and soaking the corks.
The parafin coating starts breaking down in about 1 year. We discovered this a year ago and are now rotating our corks to make sure they remain fresh. We go through about 10,000 corks a month, so it is easy to keep them fresh. For this reason, I don't recommend buying anymore corks than you will use in 6 months. This is not just and issue with my corks. It is an issue with all corks, agglomerate, natural and synthetic.
The second problem is soaking corks. Soaking corks is not a good practice. Not only does it soak off the parafin, but it softens the cork which will lead to leaking and bacterial infection in natural corks.
Most of the other corks available, even the Nomacorc, will only protect your wine for a maximum of 3 years. My corks will protect your wine for at least 5 years. Some of my wines are now 8 years old and I have not had one leak yet!
If you have any corks from me that are questionable, please let me know and I will gladly replace them.
As an aside, if you soak your corks in sulfite before inserting them, the specks could be from the sulfites.