Again, if you aren't willing to put some end-of-session detection code into every page, I don't know how you will ever track it down.
Again, I haven't seen this in many many years of using ASP.
We have one site that gets about 250,000 page hits per week and I am not seeing it there.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.