Re: 156 2.4 JTD overheated and seized?
Andyboy is right in that you probably wouldn't get much of a car for £500, a 140bhp y plate or newer will be at least 1200quid at auction and it will no doubt be in need of some work.
You can get lucky, I did at £250 for a yplate 140 veloce SW, but it really was 1 in a million.
The 140/150 jtd is more complex than an old pug xud1900, but they are still simple enough to work on yourself, Nelly has proven that.
The common rail theory is in fact very simple indeed, but as Andyboy says, the latest gen. diesels are getting more complex than ever, esp. the twin sequential turbo ones.
You should have no problem looking after a 140/150 diesel though, and even though they are not as economical as a 4pot, they are still better than petrol.
Keep looking, try and get a y-2001 with the 140 or newer engine, they are worth holding out for.