Up steps 3D to the Rescue....

[The Hat]

Thanks @Artur5, but I tried PETg once before and the results were very hit and miss, but I would like to have a go at Flexi, O’ I got a large selection of O rings from Lidl in all sizes, but I did consider using Flexi filament as an alternative.. Not yet..

I have lots of different bits and bobs out in the garden and all made from PLA and have had no issues with their quality and none of them have fallen apart as yet.
P.S. I still mainly use FreeScad for all my designs, not OpenScad..

 

[Artur5]

To tell the truth I made some 'experimental' o-rings from flex with underwhelming results. I don't know if it was because of that specific type of filament but they were no good. A flexible material is supposed to elongate when you pull it and recover the original size when you release the force. Those o-rings couldn't stand a moderate amount of force in opposite directions, without being deformed. Thus, a ring of 20x2 became 25x1.5 after the (destructive) test.
Maybe more infill or more layers was needed for a better performance but then they would end up being too stiff.