Josh - find another
300D in better condition and use your existing car for parts if necessary.
If that is not an option I would start by looking in the rear differential and see what is going on, next I would pull the axles and see what I've got. This job will eat up some time if done right and that is the only way you want it done.
The thing about a job like this is while you are in there you may as well replace alot more parts than just what you intended to replace to resolve the issue. What condition are the suspension parts in overall? At this mileage you will definitely want to look at this hardware real close and replace the worn items.
Disassembling and reassembling a suspension/drivetrain assembly is a job not to be taken lightly.