Toyota are very proactive as regards recalls, more so than some other manufacturers. The airbag recall is to do with the airbag manufacturer, Takata, and isn't just confined to Toyota. So far with the Takata airbag recalls over 53 million vehicles have been recalled globally involving at least 11 vehicle manufacturers - including Toyota, Nissan, Mazda, BMW, Honda, Ford, Fiat, Chrysler, General Motors, Subaru, and Mitsubishi. As regards official recalls which are co-managed by DVSA and the vehicle manufacturer, these only occur where the issue is safety related. An oil leak would not usually affect the safety of a vehicle. Having said that, most vehicle manufacturers have something like a service bulletin system in place where non-safety related known issues are picked up and addressed as part of the service regime that vehicles are subject to. Your oil leak, even if it had not been picked up during your winter health check, may well have been picked up and remedied at the next service, especially as it was a known issue.