It seems to be pretty rare for discounts for car parts on eBay.
Conditions. The offer entitles you to 20% off the purchase price (excluding postage costs) on items at Rolan Australia on eBay, except for the Exclusions, up to a maximum discount of $300 per transaction, during the Offer Period. A maximum of five transactions applies. Multiple items may be purchased in five transactions (up to a maximum of 10 items per transaction). All monetary amounts specified in these terms and conditions are in Australian dollars (AUD).