Valve adjustment is easy, as long as you can get to the crankshaft bolt to rotate it from there. I have rotated them using the fan blade, too, if the belt is tight enough. Used to do the valve jobs on my old Benz (1972). It's due now on my newer (1983) Benz, I've always had it done and wait until about 30k miles on it vs. recommended 15k. They always tend to get loose. You'll lose a tad of power because the valves aren't open as soon or as long as they're supposed to, and they'll get a bit noisier. They have to be awful loose to make a lot of noise though.
Worst case I've ever heard was a very old Chevy pickup my Dad did the valves on. It came in absolutely clattering away. It left smooth as a witch's rear end. He always adjusted them while running. You're supposed to do it with the engine stone cold and rotated by hand. My Dad was different.
Ralph
