So I am looking at buying a friends '99 GTP which has some issues. One day after he shifted from reverse to drive, it never engaged and he kept rolling backwards. He nows says that his car will only drive if you drive it like a manual: 1st to 2nd to 3rd on the shifter. What would cause this? It has 201xxx miles on it, and I understand that issues will occur after so many miles, but I'm looking at the best course of action here. I called AAMCO and they said maybe it's a solenoid, but I'm wondering if I should save the later expense and just get it rebuilt now?

Any ideas if it could be a solenoid, or is this a bigger problem?