I have not heard of using lacquer thinner before. I would think that since it is such an agressive solvent, that it could really cause some problems.
Brake fluid was the trick that I have heard of and used before. I believe that it may work in some cases. There are a bunch of snake oil type trany rebuilds in a can on the shelves out there.
If you have a transmission that is older and has soem potentially hardened seals, then if you pour something in that could soften a seal and make it seal better than some short term help would be achieved. Nothing works as well as replacing the seal.