The weird thing is I couldn't find the screw and washer that came out and they're not particularly small. I did notice another screw underneath the stove, suggesting the wrong screw was being used as a replacement. Again weird, as we've had the place 11 years and never noticed an issue before.
Pulled the other screw and washer to have a visual reference while ordering. This partially dismantled the oven door, which was the most fiddly part of the operation.
Screw and washer were easy to identify on the site and order came in two days, a very pleasant surprise.