Hey Miles81, don't even think about trying to replace a leaking vacuum element unless you're an experienced MB tech! Believe me when I say you'll regret it. The first thing you need to do is correctly diagnose the problem. While the most likely cause of your complaint is a leaking element, it's not the only thing that could do it. The switch-over valve unit ( located behind the carpet on the right side of the transmission "hump" ) could be faulty. This is also the place where ALL of the elements can be checked for leaks. For the rough idle, check the distributor cap and rotor and a compression test would be a good idea( I'm assuming it's a 103 motor ). For the trans shift, the bowden pressure cable should be adjusted correctly and the modulating pressure can be adjusted. My advice is to take the car to an MB dealer and have it looked over. This shouldn't cost much. With accurate information you can go back to the guy you bought the car from and maybe work something out. You'll enjoy your car much more if everything works the way it's supposed to, and the only way to assure that is by trusting the experts who deal with MB vehicles every day. Good luck