You really MUST check the chain tensioner. The plastic pads get brittle with age and break. When I checked mine 100 miles after buying it, the tensioner top pad was cracked in half and holding on by a thread.
Unless you are very lucky (as I was), the broken bits get stuck in the sprockets and then you lose some combination of chain, cams, tensioner, valves and even the cylinder head casting itself.
It's a really easy job to check, you can pull the cam cover with just a good quality 5mm hex bit. It's possible to wiggle the cam cover away from under the fuel lines without removing them.
I would replace the tensioner plastic pads as a matter of course unless they have obviously just been done. That's a job you can do on the driveway, there are loads of instructions online. All I would say is use a torque wrench that goes down to 10nm and take your time... there are lots of reports of people stripping the threads in the head. I also changed the J-tube that feeds the tensioner, the crush washers and cam cover gasket. I probably should have changed the cam chain as well... but it looked OK and I didn't fancy taking the cams out.
