Fark!
In English the normal term is piston 'ring' rather than 'spring'. (That is for those who know nothing of such things, not to correct your writing my friend.)
So, a or even some, broken piston ring/s. Fark again.
If it were my bike then Sod's law would dictate that the broken ring would have scored the cylinder bore and that would mean at least a good honing but probably a re-bore with the liklihood that I would have to go up a size in piston and that would mean all 4 being bored and 4 new piston and ring sets.
But that's my luck. You may be more lucky but knowing how long this has been going on (with your excessive oil consumption) then I am waiting for the even worse news.
Brian (who has his fingers and toes crossed for you and at least with Costas you are getting the best of customer service as well as mechanical service 😎 )
PS Give them my regards and tell them they really are special guys.