DE-1 maintenance
There are foams inside the DE-1, and like external foams on the F2 body, they have deteriorated and turned sticky. These old foams would eventually corrode through the protective paint, and then corrode the mirror coating making the prism unusable, see photos below. Since there are no more spare parts, these old foams should be replaced before marks show up on the viewfinder.
Grey/black patches showing areas where the old foam had corroded the silver coating Grey/black patches showing areas where the old foam had corroded the silver coating
Rotten foams inside the DE-1 Rotten foams inside the DE-1