1999 Subaru Legacy GT. The car can be put into Park and it holds until the key is turned off....and she will roll away

Hi there. was there an incident that occurred before this problem?

This is a fairly simple system. The lever, a cable to the transmission, and what is called a park pawl in the transmission, that holds internal components in the transmission, so the car doesn't roll.

The lights flashing is a bit of a mystery. Is the steering column loose?

If I understand correctly, the car will always roll when in Park, correct?

The end of the parking pawl engages mechanically with the gear groove of the parking gear. This gear is spline-fitted to the drive pinion shaft.
When the select lever is set to "P", the manual lever connected to the manual shaft turns, moving the parking rod backward. A cam and spring are installed on the rear of the parking rod. The parking cam slides freely on the parking rod. The parking rod and cam contact the "V" groove of the actuator (secured to the transmission case) and the back of the parking pawl. With this arrangement, when the parking rod moves backward, the cam moves to the back of the parking pawl and the "V" groove of the actuator. The parking pawl turns in the direction of the parking gear using the parking pawl shaft as a pivot. It then engages with the parking gear groove.
If the end of the parking pawl rides over the tooth of the parking gear so that the parking cam does not move midway between the pawl and actuator, the parking rod will move to "P". This compresses the parking spring so that the parking cam is ready to move to "P". Under this condition, if the vehicle moves slightly, the parking gear will rotate to engage the pawl completely.
Except for the P range, the parking pawl is tensed by the parking pawl return spring in the direction that moves away from the parking gear.