a few common faults are
water ingress to passenger footwell through the scuttle panel over the polen filter
failing aux belt tensioner, will make a drumming noise at idle
duel mass flywheels can fail and often take the starter motor with it due to the iron fileings that clog it up
egr valve and manifold can become clogged but can be removed and cleaned or blanked completley
delphi injectors can fail or lose there coding at any time giving all sorts of running problems
rear calipers can stick, can sometimes be cured by a good strip and clean
the bonnet lock can break, replacement means drilling holes into the grill behind badge.
as i say just a few common issues.