1998 Subaru Forester Rear wheels biteing on corners

Hi hope you can help, my TTB forester has developed a fault with the autobox. When i turn left or wright and also on reversing the rear wheels

feel like they are trying to brake or lockup. I have the workshop manual for the car and have already had a go at fault finding the problem.
Now it is my understanding that the duty solonide is at fault or the lockup valve could be faulty, any sugestions would be great as i am now thinking of removeing the sump of the box to see if there are any problems with the wireing.

Thanks Dave