Hence (not sure if thats spelt correct) asking the question.
8 years is a long time to not be at his previous level
You don't win stuff with a bad goalkeeper. Southall won the FA cup and 11 finals later won it again. How long do you want him to go on for?
He had a little period in that time frame 92 to 94 when he looked not quite invincible as he had previously. Probably a lot to do with the disintegration of a trophy chasing club. Make no mistake he was still a top level keeper then, just not the world's best. Then he had an Indian summer style end to his career.
In that early 90's period he was still winning us games/securing draws. Your season reviews aren't showing every save he made, every claim from a cross or corner to take the pressure off. Not every goal that is scored against a keeper is something that is unstoppable, the attacker could have given the eyes and it's read wrong, small deflections, keepers use defenders as blocks and if they don't do their job properly, you see pea rollers going in, all that make the goalie look like he is a mug. That happens today. It happened to Schmeichel on numerous occasions too.