Tranny leak (and/or slip) Trans-X stop leak?

[networkboy]

Ok,
so the critical bits are done on the Merc:
Exhaust hanger (first bolt in driveway, other bolt held on by gunk only)
Autolite GP swapped (for another autolite )

So the good:
After three months sitting, only two half dollar size spots of oil on the ground.
Float charge overnight and it fired up better than expected.

The bad:
swimming pool of transmission fluid on the floor. (about 3/16-1/4 inch below low on the dipstick after a short drive to get to temp and get fuel).

The Ugly:
My truck has *no* reverse or fourth while first and third appear to be optional (second, however is solid as a rock ).


So to summarize: While picking up some essentials for the repairs the counter guy suggested Trans-X for the truck (supposedly fixes slipping, leaks, etc.) Any thoughts? I don't really care too much about the truck, so in it will go and I'll see what happens... but for the car (since I love it, and as of yet don't have a 4 speed to swap in) how hazardous is this stuff to the transmission? Is it a case of may not help, but likely won't hurt, or is it a BadIdea(tm)?

Cheers,
-nB