It is not just the bobbins that wear down the semicircular location in the alloy disc carrier also loses its shape and becomes elongated. If you remove a bobbin you should be able to see the wear on both parts. Older discs are 1/4" thick (when new) but those now sold by Norvil are thinner by about 0.040" (which makes them the same thickness as most commonly used modern discs). So check your thickness on an unused area before ordering replacement parts.
I have the thicker type 13" disc an found this out when i ordered a new centre carrier and bobbins plus the weavey washers. They explained they had changed the disc thickness meaning the carrier and bobbins would not fit and they refunded my money with not problem once i returned the parts but im in England an phone and postage is much cheaper than for you if your in Australia.
If your disc needs grinding an the bobbin location area is reduced in thickness this will affect its fit on the carrier depending on amount removed.
I fitted the weavey washers and this has helped my disc for the time being and braking is not affected by the increase in play as yet. But i think by the time you (or me when the time comes) have messed about with centre and bobbins it may be not much more to simply replace the whole disc (i will have to anyway as parts for my older style are not available).
