Black Wombat

i was wondering if Tappet Cover Warpage is common with these engines. I have an oil leak from the tappet cover, gasket was replaced 7 months ago and my mechanic advised warpage is common. I've had the car for a year or so and it's never overheated. If this is the problem where's the best place for parts, my local wreckers arent much help at the moment. Thanks Chris