I was only thinking about this seal the other day!
If I remember correctly his/her name was Sascha, and his/her enclosure is where the Gentle lemurs are today.
Yes Sasha lived at the zoo from 1967 to 9th April, 1999 when he put to sleep due to deteriorating health. We kept a small group of African penguins in the enclosure after he died after they arrived from Artis Zoo until Seal and penguin coasts was ready. If I remember correctly, it was then altered and housed meerkats, then marsh mongoose, then Geoffroy's marmosets before the Gentle lemurs moved in.