Well, it turned out to be a non-issue. The o-ring stayed in place!!! I was able to remove the bolt, inspect & remove the filter, and replace the bolt in maybe 30 minutes total.
The filter was indeed clogged, or mostly anyway. It left a thumbprint-size area of shiny metallic particles on the paper towel when I sprayed out the filter w/ carb cleaner. I can only assume this is the aftermath of the first turbo's demise.
I won't know if the turbo survived until tomorrow. I don't want it to die during a test drive at night. I doubt my luck will hold out, but if by some miracle the turbo tests ok, there's a track day this Sunday