Quick question - I don't know if anyone here can help...

Does anyone know where I could get replacement thumbsticks for an original-gen Xbox Duke controller? I've seen replacements for the S on eBay, but none for the Duke, and the listings say they're not compatible. I have a couple of Dukes and the thumbsticks on both are really starting to show their age and fall apart. Could really do with freshening them up.

Thanks in advance!