I find that there is a level of apprehension surrounding cork seals which is generally unfounded. Cork is a great sealing material and was the only piston seal available on the early model Pelikan piston assemblies (as well as the pistons of several other manufacturers). I can understand wanting to eschew cork for synthetic seals in our high-tech modern society but don’t be too hasty. I have had synthetic seals, after decades of faithful service mind you, fail me on pens such as a first year 400 and an older 120. Like their synthetic counterparts, once a cork seal has failed, it is essentially a lost cause (barring a case of mild shrinkage from an improperly prepared piece of cork). Reviving an old and failing seal is almost alway met with failure. When in that situation, the best practice is to replace the seal.
Cork can be found on models 100, 100N, Ibis, and other contemporary variants. It wasn’t until the early 1940’s that Pelikan introduced a black rubber seal. A newer synthetic seal was deployed in the early 1950’s resulting in just about any pen produced after WWII (400/300/140/120/etc) being equipped with one of the newer seals. The 100N’s straddled this line and can be found with cork on older models as well as black rubber and even the more modern seals later into their production.