Hotpoint Aquarius Super Silent leaving stains on clothes?

When using the washing cycles some light coloured garments (white, pale blue, biscuit) come out with a slight light brown stain, roughly the colour of weak tea (just dark enough to show against biscuit coloured fabric) - in some cases its is like bad dying over a patch of four square inches, in other cases little more than a inch long line the thickness of a pencil stroke.

The washing machine is in vgc.

I have
- removed and clean the soap draw and housing.
- carefully checked the rubber door seal
- removed all paddles and checked inside
- checked the inside of the drum for machine oil, etc
- turned the drum slowly and checked through the holes left by the paddles for foreign objects
- listen when turning the drum for sounds of scrapping & catching (there were none).

None of these turned up anything.

We tried a 95C wash only (no drying) on an old pillow case and this now has a slight stain.

Any suggestions would be gratefully received.

Best regards, Philip