I need help! I have a 1990 240dl sedan. It has about 90000 miles on it. It is an automatic and whenever I shift it into reverse, the gear shift becomes extremely shaky. This came on very suddenly, which makes me think something is wrong. Countless things have gone wrong with car, I can't keep putting money into it. If this has happened to you, or if you know what is wrong, can you please give me an idea if it is safe to continue driving it without putting another few thousand into it?

Thanks!