A difficult decision for you.
I have severe arthritis in my right hip and moderate arthritis in my left hip. I also have had knee replacements of both knees, due to arthritis. (Too many marathons when I was younger). I'm now nearly 78.
My orthopaedic surgeon, who is a great guy, is reluctant to operate on my hip because of my PD and the higher probability of dislocation. My GP is not convinced of this.
Anyway my hip seems to have settled down and although it gives me a bit of pain I still manage to walk up to a couple of miles without too much trouble, providing my PD symptoms are in reasonable check
My own view is that you should go ahead if the pain is really bad and it is affecting your walking.
From a personal point of view I'm not convinced that PD exacerbates the hip problems, but I guess each PD patient has to be assessed on their own particular symptoms. Kievian makes a good point about age and I certainly agree with him about second opinions and finding out why there is some reluctance. I hope it's not a budget influenced delay.