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 : $5.50 US (registered airmail)
Europe Oceania Middle East : $6.30 US (registered airmail)
USA : $7.20 US (registered airmail)
South America & Africa : $6.50 US (registered airmail)