Just on the fact you are being asked personal questions is reason enough to stay away from the mb retired mechanic. If you weren't losing cooland and temps seemed normal, don't replace the water pump. Offering 300 dollars to "take it off your hands" seem's he might just be giving you high estimates or estimates on things not broken so that you'll sell it to him. In my opinion, I would stay away from him for any single one of the points I've made; especially the inappropriate personal question stuff. You can give your general location on this forum and there is likely a forum member who can give you the name(s) of good shops to go to. In my opinion, take your car, as is, to a reputable mechanic and ask him or her to go through the car listing the things wrong or things that will be problematic in the future so you can make an educated decision as to whether to keep this car. By the way, three hundred dollars is approaching salvage yard prices. Best of luck and I hope you're able to get your MB up to specs and have an incomporable car to drive.