Since I originally wrote this, I have put a non-standard oil in my transmission (Amsoil Series 2000).  I did it only because someone who I respect (Tom Townsend) recommended it not just highly, but glowingly.  It's done fine.  So be advised that I'm not against trying new things.  I'm just very careful about it.  Tom Townsend has a lot of credibility, so I felt safe trying what he recommended so highly.

If "better" fluids do nothing, I'm OK with that. If they actually add value and life, I'm all for that. I'm just concerned that they might do harm. There's too much anecdotal evidence that suggests just that.  I'd put ANYTHING in my trans if I was certain (that's a key word) that it would give the trans 10% more life. But if I wasn't CERTAIN, then 10% is not worth the uncertainty of what the new fluid might do (or what mixing it with what was left of the old fluid that I couldn't get out might do).  If I was fairly certain that I could get 50% more life with a particular synthetic fluid (or, again, ANYthing), then I would almost certainly go for it. 

But what increase in life expectancy are you getting from putting anything other than 10W30 or Saab synthetic in your trans? What degree of certainty do you have?  Now, let's make the equation a whole lot worse. Let's add all the anecdotal evidence about 5-speed failures after the addition of MTL and hypoid gear oil and anything other than Saab-recommended fluids. This does not seem to me a good gamble.  Sometimes, better ain't better. And messing with Saab 9000 5-speed lubricant is one of those times, in my opinion. 

I have a few rules about trying something that's "better". 

bulletIf there's published scientific evidence that says something is better, I will probably try it.  
bulletIf there's lots and lots of anecdotal evidence (NOT advertising!) that says something is good, I consider trying it.  
bulletIf there's any credible anecdotal evidence that says something may be bad, I pay attention to it. 
bulletIf there's recurring anecdotal evidence (CREDIBLE anecdotal evidence, that is) that says something is bad, I stop using it. 
bulletIf there's scientific evidence that says something is bad, I wish to hell I'd never tried it! Why do I put published negative scientific evidence last? Because it usually shows up long, long after the marketing people have sold lots and lots of product. 

And there's one other thing that factors in.  It's a global variable, and it's this: Does the thing in question need to be improved?  

bullet9000 cooling system? 
bullet WHOA!, needs help. 
bullet Bar's Leaks appears to work, so let's use it. 
bullet Spark plugs? 
bullet The stock NGKs never miss a beat if you keep them gapped properly.  
bulletHow much better can you expect of something else? 
bullet What might something else do to the DI system? 
bullet Steering fluid? 
bullet Change it every couple of years with Saab-specified and it works fine. 
bullet Why experiment? 
bullet Same for brake fluid. 
bullet Engine oil? 
bullet No real need to experiment there, but the scientific documentation of synthetic's benefits is overwhelming in my opinion, so I use and highly recommend it (particularly since I drive a turbo). 
bullet Trans oil? 
bullet Is there a problem with 5-speed longevity?  
bulletDo you hear of a lot of failures? 
bullet I don't. 
bullet And of those that I do hear of, a shockingly high percentage have had something other than 10W30 or Saab synthetic in them. 

And that's why I rail against experimentation with 9000 5-speed fluids.  I'm not even necessarily enthusiastic about "upgrading" to Saab synthetic. My trans doesn't have a drain plug, so I worry about diluting the synth with the old oil that I can't get out. And in fact, I'm sticking with 10W30 for that very reason.

I just try to play the percentages. If it makes sense to me to do something, then I try to do it. If it doesn't make sense to do it, then I don't.  Sometimes better ain't better ...