The XF was not made as a V8. It seems as though many people liked putting V8’s in XF’s. Be wary of any V8 XF. Have it checked over professionally. Same for LPG XF’s. The XF was the last of the big square Falcons, even though it had rust issues, they were not as severe as the earlier models. Electronic Fuel Injection was still relatively new in the XF days so you can expect a few teething issues there.
Blown head gaskets
Cooling system issues
Oil leaks
Be wary of aftermarket LPG systems
Faded paint
Rust on wagon tail gate
Air leaks
Failing distributor
Be wary of V8 models