Oops!
The blade seal I ordered was great. But... I'd ordered the wrong part. 😮
Turns out what I "thought" I'd ordered is something else. I probably actually need a new blade unit, as it is the shaft under the blade seal which had perished, and has broken up and fallen off.
I guess I'll have to save a bit, to buy the whole blade unit.
Still loving my "Thermy" though. 😀