This is Mamiya M645 Light Seals foam (backdoor gasket sponge and Mirror Cushion) replace kit.
(This item is "custom kit", NOT Mamiya brand-name parts.)

This seal kit covers whole Light seals as below.

The price is 12 USD.
2 seal kits (for 2 cameras ) included in 1 set.

Shipping Fee Asia : $7.40 US (registered airmail) Europe & Oceania : $8.40 US (registered airmail) South America & Africa : $8.80 US (registered airmail) USA : $7.20 US (non-registered airmail) Australia : $4.60 US (non-registered airmail) Canada : $4.60 US (non-registered airmail)