I tried to refurbish an Osculati Utility
Bilge Piump 1619350 12V/8A
I could remove the two shorter screws of the impeller cage's plate without any problems but the 2 longer ones got stuck.
WD 40 for 2 hrs did not change anything.
heating up the cage did not make them move too.
So both screws broke.
I think this is a designed feature to urge the buyer to throw the scrap away.