It should say somewhere on the pump as to what pump it is. Look on the underside even. Most of them even have serial numbers. If you can't find any info, try calling Medela and a rep will help you, I am sure.
That said, if the flanges (cups) were hurting you, it's most likely because they were too small or big for your areolas/nipples. Quite normal. You may have to order a size up or down (you can order the flanges on this site, I believe or at least see them, and again you can ask a Medela rep - I know Babies R Us carries some as well usually).
In general, an 8 year old pump should be okay to use as long as it works correctly. If you feel you aren't getting the output you would with a better pump, then I'd either rent a hospital grade (Symphony) or purchase a new Pump in Style. :)