The most up-to-date list specifically for the 9241 that I've seen is "V232 HDD list for 9241 [a la ViP612]" from August 2009. Firmware is now V238. I think the new firmwares add drives rather than remove them, but the problem is actually finding one of those old ones. There are a few sites that claim to have some of the Seagate models that are on both that list and the 9242 list. You have the advantage with a US shipping address.
eBay/PayPal are very buyer-centric these days so if the listing specifically claims it works in the 9241 you should be able to get your money back if it doesn't, though you may have to return it on your own dime.