My 1999 Merc Sable started leaking trans fluid it wont go forward or reverse can i just add tansmissin fluid

They rust, the hoses crack. Replace both.

on most cars, you need to change the neutral safety switch. this car has a neutral parking position sensor, you can find it for v6 not v8, it also fits a saab 9-3. it is the same thing, a different style. however, check the transmission fluid level and troublecodes for p07xxs. reset the code and use the transmission dipstick by dorman add lucas auto trans fluid, not stop slip to the fill line. most of the time it's not the solenoid, but the auto trans plate, overfilling the fluid can cause it to trigger a check engine light, and the fluid leaking onto it can cause it to be permanently damaged, it's more than $400 for the part. lucas works in the 722.xx transmissions, most , all, clks 99-2002, just make sure the tranny model isn't a 238. i like it better than atf 134. However, these parts are very heat sensitive. fill the trans fluid, reset the troublecodes, do a general motos drive cycle from obdii.com if it doesn't drive good after four times, change the neutral safety switch. :)

You raise the front of the car & support it if necessary,
to put a bottle under it,such as an old washer fluid bottle

Then remove the steering pump return hose from the fluid
container

Put that hose into some plastic tubing & into the empty bottle

Remove the injector fuses, so the motor gets no fuel

Crank the motor & the old fluid goes into the bottle


Add new fluid Dex/Merc or Mercon V to make sure the
container has fluid as you flush out the old

When done,return the return hose,clean up & start the motor
Turn wheels lock to lock a couple times,put it on the ground
& check the fluid level

Change trans & power steering every 3 years or they will
fail for sure.

Those two fluids will not remove heat after 2 or 3 years
in service.

If you are sure the shifter is connected to the transmission, it could be a long list of things inside the transmission.

I have a similar problem. Did you figure yours out? I think it might be the pump in the trans.

Yes the front pump seals on long extended drives xway very hot it can expand have seen this a lot in my trans shop over the last 20 yrs the trans will have to come out to repair this. big job!

its impossible to lose that much fluid with out a leak. the was so low that it has burned your clutches out. would have to rebuild or replace entire transmission

well its a ford product all I can say is get the trans rebuilt-its a common problem after 130kmsof running

ASE Mechanic:
Try checking the fluid level first, and then look for any leaks. if corrected right away you might not have to rebuild the trans. but other wise look into the cost of a rebuilt transmission.

just have someone look at it. like aamco or someone that does a free diagnostic. the tranny will probably have to be rebuilt.