The M62 doesnt have a timing belt, they use chains. They dont need to be changed until way over 200k miles in most cases. The car will require basic maintenance and should cost no more than 1k a year to maintain. Altho, since you're buying the car used there are several things you should check before you purchase the car, such as the power steering lines, look for red fluid on the ground, ATF, models without self leveling use ATF for power steering fluid and a lot of them leak. Check the cooling system, including all coolant lines and radiator and neck. Check if the radiator was replaced, if it wasnt, it'll likely have to be replaced soon, you can check for a stamp on the left side back of it where it's stamped with a part number and date. Drive the car and make sure the transmission is smooth and doesnt whine. As far as electronics go, the only common problem is the loss of pixels in the cluster MID, which can be fixed fairly easily but removing the cluster and cleaning the contact points and connectors inside.
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