Espio 140m

Hi,
Could any one please help me. I have a 2 year old Espio 140m which has until now has never let me down.
On some of the last 3 or 4 films I've had developed I've noticed that the top left and bottom right hand corners are shaded to various extents. This seems to be random and in some cases blocks out 1/4 of the picture and sometimes only just shadows the vey corners. I've tried different films at different developers but it makes no difference
I assume it's the shutter causing this but don't know.
Can anbody tell me the cause and if it's curable please.

Many thanks,
Steve

I checked with Pentax UK service dept and here's their view: "There would seem to be an obstruction between the rear lens and the film plane. This could be caused either by the panoramic blinds sticking or by some other obstruction in the zooming barrels. In most cases this kind of problem will be repairable."
Pentax UK suggest that the camera is sent to them for repair.

Thanks for you help Peter.