Forester 2008 steering tightening up in hot weather?

[PeterH]

Hoping someone can give me some advice. My Subaru Forester has an issue with the steering. It seems more prevalent in hot weather when the steering gets notchy. You can position the wheel in a direction and it will stay there - its as if the power steering has stopped. No noise and no leaks. The power steering is "working" but difficult to keep in a straight line due the steering being sticky. Not an issue in colder weather???? I can only suspect pump or rack - any takers please.