Not sure if this is the size you need but you can buy just the gasket.
http://store.summitracing.com/partde...5&autoview=sku
If not here is a cap that looks exactly like mine not sure of the size b/c summit doesnt say.
http://store.summitracing.com/partde...5&autoview=sku
If all else fails try giving JL a call. Im sure he can hook you up.