My son put our 1993 STS Seville in park while driving about 25 MPH, Known Issue results: Car rolls while in park. CV Half Shaft seems it be broken with in outer boot. Also if he holds the CV shaft between the boots he can spin shaft while in park. Question is there a park lever gear or ratchet devise that could be repaired without removing trans? Could the main FWD Drive chain have snapped?
He is 18, he wants to fix the car but we do not have GM service manuals. Does anyone know these answers? Thanks...

 

sounds like the cv shaft is the problem. Usually if you have the car raised off the ground and spin one of the front tires in one direction the other one should spin in the opposite. So while on the ground the car cant roll away. So if the shaft snapped or is broke it will most likely be the reason for your issue of the car rolling while in park. But untill the use the Emergency park brake so your car doesnt roll away and stay away from steep inclines when parking.