93/94. The Dundee Utd game ( a home defeat) was down to a Sieb error. Then we drew at Raith and lost at home to St Johnstone. Five points dropped and we finished third, four points behind Rangers. However, it was eighteen league clean sheets, and one in the league cup, by Sieb that got us that close.
For me it's a very close call between the two but Sieb was at his peak then while Ruddy will get even better.