Individual replacement seals for the piston of the Pelikan 400 are not sold on the open market. That leaves two routes: a repair by the manufacturer, or an identical donor pen as a source of spares, which can often be picked up cheaply second-hand at auction. The same seal is also fitted to the M200, so an inexpensive M200 is a candidate as a parts donor.
A factory repair is the safe route as long as a model is still being built in largely unchanged form and current parts fit. As of 2010, overhauling an older 400 cost thirty euros; alternatively, a new M400 was offered against a payment of 135 euros and the return of the old pen. With models a manufacturer discontinued decades ago, by contrast, spare parts are no longer to be expected.