I may have the answer. I was concerned as the camera was serviced within the last 6 months and so hoped for operator error as opposed to a return to the menders.
When I used the winder I purchased recently, that involved taking out a cap at the bottom of the camera and screwing it into the winder for safe keeping. When I took the winder off later, I didn't put the cap back and there is a big hole right into the bowels of the camera. It may or may not be this but it could well be. I have posted a link to a review where the reviewer highlights this as a potential problem.
I mention all this as it may help other people in due course, if not me.
The reviewer is
choeN a Expert from London & KL
and the relavant prose is under "weaknesses"
The link is
Pentax LX Reviews
John