Your S.T.Dupont pen does not need much maintenance. To restore its original shine, you can clean it using a soft cloth (never use solvent-based products).
For all silver-plated parts, use a special silversmith’s cloth. Silver is a precious material that can show signs of oxidisation. Oxidisation is a natural phenomenon that can be heightened if your pen has prolonged contact with leather or rubber.
Only the fountain pen requires special attention: S.T.Dupont cartridges should be used if possible. Remember to clean the fountain pen’s feed regularly. Use the converter to circulate cold water in the capillary, repeating the piston effect until the water discharged is clear. To prevent leaks during air travel, fit your pen with a new cartridge or a full converter and transport with the nib upwards.