Strange, I remember them on the mountains too, obviously wrong thoughA sloth bear playing with a boot (for some reason my memory sets the bear on one of the mountains, despite the fact they never had access up there).
Don't know when it was but I remember seeing a sealion in a large tank in the aquarium, apparently they were testing it for leaks. I also remember seeing the elephants being trained, one of the keepers spoke to them in Hindu (?). The rhinos were also there at this time. Finally, I remember seeing the penguins in their old exhibit.
My earliest from Whipsnade? Following the elephants whilst they were on their walk and seeing a sealion pup