Thanks to all for your advice & comments
Pres-I had a closer look at the screw itself and the hole in the wheel head but there's no obvious wearing on one side....
The axle is steady when spinning at full speed ( thankfully!)
Synj00- I use marine ply bats and throw tall vessels with a narrow foot- afraid you can see/feel the tilt in the wheel head when centering the bat at full speed-( no pins) I didn't notice the tilt at first-and have used the wheel for last 7 yrs-but was finding things a lot harder to do! It's only off by about 2 mm and gradually getting worse- perhaps for smaller pots & no heavy bats, I wouldn't have noticed for much longer
I'm the 3rd owner that I know of- but it may be 4th,5th pre owned! But she's a beauty, like an old friend where you know every creak & squeak!
Tom, I did get in touch with the makers who then suggested I may need a new wheel head!
I've been googling & utubing looking for anyone with a 'worn wheel head' - unfortunately not..
JRGPots- like your literal take on it!
Out of necessity- went & got some heavy axle grease and put big dollop onto axle top- refitted the wheel head and screw/pin..
All good so far!
fingers crossed-only throwing mugs at moment so nothing heavy or taxing..
and she hums beautifully now again!
Hopefully have cured the tilt- will be certainly keeping a close eye now- taken for granted for too long!
Thanks again for all your advice