Our "good" car is a '99 ML320 with 244k miles on it (it's been a great vehicle for us for 4 years now). A couple of weeks ago, it started making a bad clicking noise upon taking off. An independent mechanic looked at it and he thinks the transfer case chain is slipping. After poking around further online, I feel confident he is correct. Right now, we can drive around and accelerate gently and I guess the chain is not slipping (at any rate it's not making the noise). Question: can we make any reliable predictions about what's going to happen if we don't do anything? Will it get a lot worse soon? What would be the worst case scenario? (We got the car for cheap so there are limits to how much we can invest in repairs for it. I understand there are people who have simply replaced the chain so this is one course of action I've been thinking about.) Thanks for any comments/guidance.