Hello, I have a 2015 subaru crosstrek with 85000 miles and a rebuilt title. I recently had the AT OIL temp light come on with a few extra lights like ABS, and hill start assist. So I thought my transmission was overheating or something. However whenever I scanned the car I had no codes show up (the light would also disappear if the car was turned off and back on again).

So I took the car to a subaru dealership and they told me the valve body needed replaced. The code they said they had was P0971. So, not wanting to take apart my transmission, I went ahead and had them replace the valve body. It cost $1400 for it to be done. After they had it done they test drove the car and noted that they felt the transmission slipping and that I could have a check engine light come on and codes saying that "there could be low pressure in the transmission" essentially. After turning the car on, while still in the lot, all of the same warning lights came back on that I had when I innitially took the car in for a repar. Except now the check engine light is on too!

So I go back in and they scan it again and have two new codes P0841 and P0700 (the old code was suppossedly gone). They now tell me that to fix it they'll have to replaced the transmission. They claim that adding the new valve body "corrected the pressure inside the transmission" or something, and thats why the transmission is slipping now. My question is: Is it common for transmissions to have slippage after simply replacing a valve body, or did they destroy my transmission and want me to pay for it? Upon driving it off the lot I can see that the slippage is really bad and basically non-drivable, unless I want it to break down on the side of the road. They even advised me not to drive the car!!! Mind you, I had no slippage when I took the car into the dealership. The car drove PERFECTLY fine, except OCCASSIONALY had the AT OIL temp light come on every 30-100 miles or so. I don't know what I should do. 

Thanks in advanced!