1990 S3 S type start base strange shape causing sliding

[Aladoro69]

Does anybody have an issue with the old S type seats and a feeling of sliding forward?
It's as though the seat base shape is like a bowl with particular emphasis at the back
This seems to cause lower back/bum to rotate and slide forwards
It looks as though the foam inside the base at the back where it meets the seat back is too high and the centre section too low in comparison
It's bad for the driver but particularly bad for the passenger with nothing to brace feet against

Anybody experienced this and if so why fixes it workarounds?
Thanks

[BertBert]

Could it be that the foam in the seat (base) has rotted and needs re-upholstering?

The foam in my 90's bench seat bases was completely rotted away.

[Aladoro69]

Possibly
The only thing against that is that both seat bases are virtually the same and would be surprised if wear was so similar
Does anybody with S type seats have same feeling or not?

[BertBert]

But it's probably rot not wear. The two bench seats squabs on my car were equally rotten