Newbie 2000 C70 Transmission

[Joedeec70]

I had a 1999 C70 it ran great. The top never worked. This morning I am going to see a 2000 C70. The transmission service arrow is on.
The gentleman told me the car shifted fine. Then after an hours drive, it became stuck in low gear. After sitting it was OK. Then after driving it became stuck in 3rd gear. I don't yet know at this time how long he drove it in 3rd. I know from what I have read that could be bad.
It has been sitting he says he has not messed with it since.

The car has 90K on it. He is asking $1350. I don't have much time. I am going to see it this morning.
My question is what steps would you take in an attempt to rectify this before biting the bullet & bring it to a transmission shop for repair?
I would reset service light. Disconnect battery. I only have an OBD code checker. I would flush the transmission. With the addition of Lucas or Prolong. I know some people hate additives. Would the PNP be a possibility? Is any other resets possible?

Any help would be greatly appreciated. Since I don't have time to search the forums. Otherwise, I would.
I have tried to do some research.

[abscate]

If you are set on buying value this car , budget about 3500-4000 for a transmission swap with a good used one without guarantee.

[bmdubya1198]

I'd make an offer on it if you really like it and it's in really nice shape otherwise. The 2000 should still have the AW50-42, so those transmissions are pretty good overall, unlike the newer AW55 5 speed auto. PNP switch is very possible, a good way to tell is to move the shifter back and forth several times (PRND3L) and usually if it's the PNP switch, it'll go back to normal. Granted, this doesn't always work and it won't last, but it's a fairly good test.
The best thing to do is to hook it up to VIDA and read the transmission codes. Worst case you could be out the cost of a new transmission (I feel it's unlikely, but I wouldn't rule it out) and best case, $50 for a PNP switch.

Transmission drain and fill is a good idea either way, who knows when it was last done at 90k miles... possibly never. I would urge against using an additive, I wouldn't risk damaging the transmission with anything like that.

[erikv11]

How'd it go, did you buy it?