I'd check the retaining bolts for the camshafts. They tend to work loose and allow the camshaft(s) to break. That results in the valves meeting the pistons - very expensive. If it is happening to your wife's car and you catch it before a camshaft snaps you'll save yourselves several hundreds of pounds.
Subject to a recall by Vauxhall recently because of the number of failures - have you received a recall notice to get the bolts checked for tightness?
Other than that it could be the cam-chain. These cars have an every two years service regime which i.m.o. is too long between oil and filter changes. Regular and frequent changes keeps the oilways clear and everything lubricated properly. Missed changes and contaminated oil can lead to blockages and premature wear.
ChicksFan, April 2011
