I have a slow leak on my 83 RX, I have taken it to the trans place like 4 times becuse after about two weeks it starts to leak again after they said they fixed it. The guy told me that there is something wrong inside, does this sound right?
He also told me that it would cost between 600 - 900 dollars since they would have to break open the trans. Is this the right price to pay?
P.S. the leak is on the top of the trans.

 

The top, where? If it's by the shifter, it's probably the rear seal: $3 and 45 minutes to change it.

 

It has been changed twice, and still still leaks.

 

Really? Well, look at the driveshaft and the tail-housing of the transmission and make sure that they're not damaged. If you can't fix 'em with gasket sealant, both are easily replaced. Also, you might consider going to a non-synthetic gear oil since those don't seem to want to leak so much. I'm not sure why.

 

There is a transmission vent valve to check. If that thing isn't working pressure builds up inside the tranny and leaks out the rear tailshaft seal.
The valve is located infront of the shifter on the right [passenger] underside about 2'' down.
My transmission leaked out of the rear for 4 years until a mechanic friend pointed this vent out to me. I changed the rear seal 3 times myself and had 2 others change it once each.The car only leaked about 1liter /year so I wasn't too worried but the hypoid oil leaking on to the catalytic converter really stinks badly.
Good luck.