There's plenty of used parts, because of Cash for Clunkers.
If you don't have an owners manual, theres plenty of those in the salvage yard too.
I bought a Jaguar S Type Jag from local craigslist years ago, and put all the fix's on AF.
If you can pull a p-code and use google, you can fix it!
Google ''Troubleshoot Jag P0420 & P0430''
Did he knock the cluster out trying to fix the CEL?