I recently got a 1968 Dodge Monaco with the 383 and the owner told me that the transmission was good but that the car had been parked for years, yesterday I started checking the car and when I was checking out the transmission I noticed that at first it did go through the gears and all, but after a while the wheels stopped spinning and it wouldn’t shift. Before starting the car I had put TransX for the transmission. I’m afraid I will have to buy a new transmission, does any of you have an idea of what it could be?

 

Check the trans fluid in Neutral with the engine running to make sure its within spec for fluid level....

 

Carlos -

Assuming that you have "enough" fluid, as Bob said, you might be looking at a rebuild, or at least a flushing.

Back in the day, we just assumed that using any "leak stop" in your trans meant you'd be getting a rebuild in the near future - yeah, they just gummed up the works.
If you're able, drain the fluid, drop the pan (examine the fluid) and remove the valve body.
Make sure the band retainers are where they are supposed to be (you should be able to google a picture).

IF everything looks right, consider a flush, just remember it won't fox a real problem, but "might" fix the leak stop thingy.

Archer