Assuming you have access, try taking a piece of wire (like piano wire or heavy gauge guitar string) and cut through the 5200 under the washers. Use a couple of pieces of dowel as handles. If you can cut through under the face of the washer the edge bond should be breakable.
I think there are 5200 solvents, but you may not want to use them in that area; you really only want to get the washers out, not risk attacking the rest of the seal.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"