The most reasonably priced component used on the Vt1100c3 Shadow Aero 1999 (x) Germany / 34p Gasket Kit (1) is the Washer Seal, 6mm.
On this parts fiche the Washer, Sealing, 10mm is the most specified component.
A sample from the products for the Gasket Kit (1) include: O-ring,29x2.4, Seal,water Pipe, Seal,water Pipe, Seal,valve,stem.