The replacement TC will have the same wireless chip.. latest TC is broadcom.. I think they have serious issues with atheros chips used in a lot of other devices.. even some macs.
Let me suggest taking the manual approach.
Setup wireless again.. if using lion download and use 5.6 airport utility.
Give wireless names that are short .. no spaces. pure alphanumeric.. that is important for the PC world SMB.
The 5ghz name should be different from the 2.4ghz name.
Set the wireless to fixed channels, 1, 6, 11.. try each in turn.
if that doesn't work.. change the wireless mode from auto to a/n - b/g (you can apparently hold down the option key and have other settings here).. by reducing the 2.4ghz speed to G wireless it will sometimes work better than at N lite.. which is all apple allow anyway.
Do the above testing with security off.. just while you do it.
Put back security wpa2 personal with 8-12 character pure alphanumeric passkey when finished.
If you don't get anywhere.. use an N or G wireless router as an AP plugged into the TC.. Just a very cheap one will work.. set up in wan bypass.. ie plug lan TC to lan router.. turn off dhcp in the router and fix its ip to match the TC .. eg if TC is at default, 10.0.1.1 then make the secondary wireless 10.0.1.254
Set a different name and lock the channel for the AP so the SMB devices can reach it rather than the TC.