... 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.
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.
Yes - this is true. However, I'd rather not have to dismantle my 9241, currently working fine, in order to verify a new drive that I purchased on ebay. Or spend $120 on a drive and leave it there for a few years before testing - and maybe then finding it doesn't work in my receiver - and have no option for procuring a replacement.
So, given there is a whole list of suitable drives (above), then any drive that is currently installed in an operating 9241 should also work in mine? With 9241's that cannot be activated going for $50 on ebay, maybe that is a better way to go? OK, the drive won't be "new" - but it will presumably still be pretty new, and there is no doubt that it will work in my 9241... when the day comes that my original drive gives it up??