Possibly they refitted the old seals and added sealant ? , when I changed the ones on my Jeeps 642 engine to the purple ones the original orange ones were like new but if you refitted them to the cooler and ran a straightedge over them you could see there would hardly be any compression when torqued down for them to provide a seal.

My bad just realised seals you removed were purple ones so maybe the sealant stopped them from sealing properly ?