Many valid points discussed above. Ebay is indeed a good option due to the sheer number of users worldwide. Personal take, bar is probably generic but it is vintage and getting uncommon so there will be collectors out there. I have read online comments on other bar from the same range, saying the logo is an older version (have not done own research on this though). In normal circumstance, think it should be tough getting 5% or more over spot. But who knows, it takes just one keen collector at the correct time and you'd be a happy seller. I guess that's where the "best offer" function may prove useful. Ultimately, you'll need to look at the price level you acquired the bar and whether you'd be comfortable with the profit made (with modest premium estimation) after stripping off items such as auction fee, if any.
Just for reference, an ebay germany listing for a smaller 10g bar in sealed plastic ended this morning with around 8% over spot. Link:
http://www.ebay.de/itm/10g-Gramm-Go...D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557
Good luck