wiki.answers Did Lucas..
Things you should know: Chart.
Differences between quality & poor-quality additives.

From: wiki.answers Did Lucas worsen my transmission problem. Web address below.
Question posted at Wiki-Answers.com
Is Lucas transmission additive any good I used it twice in two 
different Chrysler transmissions which had some problems and 
they died 3 days after Was this a coincidence?
In: Chrysler Concorde [Edit categories]
Answer: Why it Failed
Transmission fluid must circulate freely and in great quantities 
to cool, lube, maintain pressure the system needs. Restrictions
 to this can ruin a transmission in short order.
Additives solve many transmission problems. Some brands stop seal
 leaks. Other brands smooth rough shifting, speed up slow shifting, 
and cool in several ways - reducing hot-spots of friction,
 and by removing a coating residue, which permits heat transfer
 to the outside.
This is what I think happened.
A good additive would have more or all of those features, and a 
less desirable one would have less. I have lots of experience
 selling different kinds of additives and I get feedback on all
 this. This is what I think happened.
Lucas is a honey-like liquid. If this substance was added to the 
transmission with the motor off, no transmission fluid would be
 circulating. The Lucas product would not have had opportunity 
to be agitated and blended in with the moving fluid. It would
 just sit there at the bottom - where the fluid pickup screen 
is located.
That would mean trouble maybe. Lucas could choke-off the the 
 fluid inlet - as that is where the fluid inlet opening is. What 
Lucas was sucked up, if any, when you started the motor, may 
have been so stiff it may not move onward. Or not flowed like the 
watery transmission fluid would. Maybe, it blocked the flow.
With no fluid in great quantities flowing, due to the honey-like
 nature of Lucas, or if the Lucas product was a solvent, 
not the honey liquid, and the solvent washed the guts of 
the system clean, bits of sludge containing clutch fibers may 
have floated free and these could have choked off the screen, 
and blocked the transmission fluid flow.
Other than bad timing in your case - twice in a roll, those are 
two often-seen conditions when the transmission is taken apart,
 inspected, and rebuilt.
Good transmission additives, those made from a quality standpoint, 
would have an ingredient called a dispersal - in addition to the 
ingredients needed to clean, cool, free sticky parts, friction modify, 
and so on. Doing so holds residues removed in liquid form for draining. Residue removed in this way prevents their blocking of the oil lube pickup tube and oil delivery in your transmission and engine.
End. wiki.answers Did Lucas...
An explanation of such products are found at these 3 web sites. 
Transmission additives, Review, more... 
Transmission-remedies. More... 
Transmission Help, Tips 
Wiki-answers Did Lucas hurt my transmission - Where this article is quoted from..