What might cause mazda cx7 turbo oil leak?

Mazda's CX7 series engines are earning a reputation for variable valve timing (vvt) defects that can cause oil leaks, excessive smoke out of the tailpipe, loose timing chains, and catastrophic engine failure. Mazda has acknowledged the vvt problems in a special service progRam but, according to owners, has denied warranty coverage in some cases.Oil is almost always the main cause of a VVT solenoid going bad. Most often, the old oil is the culprit. As oil goes through an engine, over time, the combination of heat and small impurities cause the oil to thicken. If it goes on long enough before an oil change, the consistency of the engine oil is comparable to sludge.