On my 83 300D turbo I have the same squeak from the right front. I have decided that it is the ball joint that needs to be replaced (I lubed the open ball joint and my noise went away)

I do not hear a squeak when the cars weight is off the ball joint, only when it is fully loaded.

Sounds like you are on the correct trail with what you plan to replace while the car is on jacks.

Good luck,

Wayne