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.
1984 Fast/Nicholson 345 "FastForward"
".. 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)