Use code 25OFFOIL (Online & Instore) for engine oil discount.
30% off Car Audio (Instore Only)
This deal is also valid on their eBay store(stores.ebay.com.au) with the 25% off + cashback + $50 voucher - Credit to Willy Orwontee for alerting me to this-
(Example of what I purchased: MOBIL 1 SYN 0W40 5L ENGINE OIL ($105 Reduced to $78.74) + Eagle One A2Z Wheel & Tyre Cleaner 160ML ($16.99) + HPM Slimline Double Adaptor 2 Pack ($5.66 Masters Store) = $ 101.39
With voucher, cashback & oil discount = $180.17 worth of goods - Save $78.78
Remember oil lasts up to around 5 years and even longer if unopened, so even if you don't need some now the discount might help your future self in a couple of years time (as long as you haven't bought a new car by that time obviously!)
Looks like it's also available on their eBay store with the 25% off + cashback + $50 voucher per here