I would love a 116 SD... FYI, that is the body style you have I belive. very nice style IMO, HOWEVER, to keep this car in good condition, you will need to learn a bit about working on them. if I were you, I would start at the link that says "last thread" and start browsing the headings for something that looks like what you want to start on, and read all the questions and replies. also, a good service manual will help with some of the problems you mentioned.
pick one thing and start working on it. I would start with the door, search here for remove door hardware. or something similar. then when you find the problem and fix it, move on to where the radiator is leaking and find out where it is coming from, autozone will loan out a radiator pump up kit and you can work with cold engine to find where the fluid is escaping and if it is a hose, replace it if it is the radiator itself, it will be a bit more money, but still just a R&R. trust me, the guys and gals here on the forum will bend over backwards to help. we love the MB and those who love them.
in no time you will be up here helping others with their MB's problems.
welcome to the fold.
John