1993 W124 300D that I have owned for about six months and 28K miles has always had a thunk/clunk in the rear end.

It only does this when starting from a stop and until yesterday it was "just" the thunk/clunk.

Now it is more of a dull grinding/binding sound and I am pretty sure it originates from the driver side axle that I recently noticed had a torn boot on the differential end of the axle.

My next question is, what is likely to happen if this is the problem and I have a catastrophic failure?

I ask because I have a 375 mile work trip planned for tomorrow.

I can reschedule it(luckily) but I would prefer to not miss it if possible.

How do you check if an axle is bad?

Could it be the differential itself?

I replaced the oil in the rear end a few months ago and it looked fine with no noticeable metal in the old oil.

I don't know for sure how long the boot has been torn either.

I do know that it looked bone dry when I noticed it a few weeks ago.

I didn't see any tears in the other side and I am pretty sure that the sounds I am hearing now are coming from the driver side.

Is this a job where I should replace both at the same time or should I just replace the one with the torn boot?

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1993 W124 300D
-297K on the clock as I type this.