I had a MUJI “soda-glass airtight jar” (1L, made in Italy). Looked great; I stuffed dried kombu in it. The lid was stiff, so I switched to zip bags and shelved the jar. Later, the gasket had browned and cracked—no seal. MUJI’s shop search failed, but customer service says spares are ¥105 and must be ordered via stores/phone.

Amazon showed orange gaskets from Le Parfait/WECK; white ones (Cellarmate) were ~¥194 + ¥540 shipping (Tokyu Hands). Not ideal.

Cellarmate Replacement Silicone Gasket for Airtight Jar (White)

Seisho

IKEA sells 5 white gaskets for ¥199

Since I had IKEA jars, I checked: the gasket set shares the KORKEN name. Link: http://www.ikea.com/jp/ja/catalog/products/80247535/ —5-pack, ¥199. I grabbed a pack on my next trip; it fit the MUJI jar perfectly.

These jars seem standardized; likely fits Le Parfait/WECK too. White gaskets at low cost = great for swapping stained/smelly seals (kombu smell lingers).

Diameter: ~9.5 cm.

Thickness: ~3 mm.

Made in Germany

The glass jar is China-made, but the gasket said Made in Germany. Germany has lots of rubber products (tires, etc.), but why not Poland/Czech (cheaper)? IKEA is fabless—outsources manufacturing—so maybe a supplier cluster in Germany. Who knows.

Rubber-company counts (EUROPAGES search “rubber products”):

Country	# of rubber companies
Germany	751
Italy	867
France	586
Belgium	58
Slovakia	46
Poland	891
Denmark	82
Sweden	18
UK	772
Ireland	16
Spain	240

Poland is biggest nearby (EU’s factory). UK/France/Italy also high; Sweden (IKEA’s home) is low. Regardless, the German gasket works.

Takeaway

If your glass jar gasket yellows/cracks, IKEA’s KORKEN pack is the cheapest white replacement. If no IKEA nearby, MUJI/Tokyu Hands sell singles for ¥100–¥200. Five spares at once can be overkill; singles are fine if you don’t need extras.