In addition to the advice that Guinevere has already given you, if you haven't already done so it may be worth doing some searches for an identical item being sold by other sellers, making a note of the seller's feedback rating and the item's overall price. Ideally you want to get a seller with a high percentage of postive buyer feedback and a low asking price for the item, but you'll have to do a bit of research and compare the various options to ascertain which seller would be the closest match to those requirements.
Once you have done this put the item on your Watch List, making sure that it isn't being sold by the same seller who has so far failed to send you the item you have paid for! If you do have to get eBay to step in and help and they end up forcing a refund you can then purchase the same item from the second seller, whereas if you do eventually end up getting your item from the first seller then so long as you are happy with it and don't feel as though you have any reason to return the item for a refund you can delete the second item off of your Watch List, unless you want to buy an extra one so that you've got spares available in future for when the parts you need for your motorbike start to become difficult to find.
