Another idea, liquid silicone available everywhere. Spread a bead of silicone around the underside of lid, wipe with your finger to make a smooth and even layer, wipe off excess. Allow to dry to the touch. Will adhere to the lid and the contact surface will remain flexible creating a complete closure of lid to top of inkwell.
I saw this at Home Depot, probably available everywhere.
Made of 100% silicone, the GE 2.8 oz. Silicone Sealant provides a watertight seal around doorways and windows and is ideal for marine applications above the water line. The sealant can adhere to plastic, glass and many other materials and dries to the touch within 15 minutes.
UV-resistant, translucent silicone
Adheres to plastic, glass and metal
Dries to the touch in 15 minutes and hardens in 12 hours
Hope this helps, let us know what you use.