Yeah to be honest I'm just gonna take the 9 quid hit for the side panel...it would cost me money to send it back so not worth it. Plus I could make the current side panel into a windowed one quite easily at work. Xigmatek list a window version on their site but from what o can see don't sell one yet.
Return the case panel under the DSR, they HAVE to by law refund all postage (even return).
If you're unaware read up on the Distance Selling Regulations, OcUK are one of the best companies to play by this rule and actually doubled their own DSR time to 14 days. The likes of shitty "companies" on ebay wouldn't of course let you know about this, or even refund the postage.
They're the top place I use and use them for a reason, the support + community is second to none.