Jeff...
I had EXACTLY the same problem for over a year... getting worse and worse. I replaced the clutch (was stiff... turned out to be the throw out bearing collar or some such thing), I replaced all linkages... to no avail.
I was about to buy a new used tranny and figured I would try the redline fluid. The fluid that came out was basically brown crap.
Needless to say nobody was happier than I was to find the problem was immediately fixed! (except for Bruno who would have had to put the tranny in)
It's been in for over a month now and hasn't recurred.
You can get Redline in only one place that I could find, it is called JRP Johnston Research and Performance, Mississauga, 905-564-8805. www.jrponline.com
You'll need two bottles @ about $20 CDN each. It's worth it.
Good luck!
Rod