Tyger, what is that? Sorry for ignorance.

Guys couple of issues:

1) I again tried showing to mechanic( he didn't know how to work on these, he said) and when we tried to rotate right rear wheel, left(behind driver) rear wheel made some sound. But if you just rotate left rear wheel, then there is no sound.I don't know if this becomes that bell type sound, I hear when I drive at low speeds and go over uneven road.
The left rear wheel axel has some play going left-right-left. Right rear wheel has no play. The left rear wheel also had some rotation in stationary position but right rear wheel doesn't move.
Left rear wheel has can type axel and right rear wheel has bolt axel. The axel boots don't have cracks.
2) I think I definitely have vacuum issue as sometimes, my central lock/unlock works,sometimes it doesn't. And my trunk opens accordingly if the vacuum has unlocked the car.Is it major issue expense wise?
3) In my first two weeks of ownership, I had not very often issues with starting the car. But now since yesterday, I have to keep trying a lot until my key moved from initial motion and start the car. I have noticed that the initial my key doesn't line up groove(the first of three notches) on tumbler( the place where you insert the keys)when I insert the key.

Now, I would like to mention that I got two keys from the seller, one key which seems a bit worn out opens driver door and trunk but doesn't open other side door or start the car( this key has something written MBxxx) and is a bit worn out. Other key starts the car , thats it but doesn't have anything written on it. It seems okay and doesn't really show wear and tear. The plastic of both keys looks similar.
What keys are these? Is my tumbler not original?
PLEASE see that I had so much trouble today, that I left my ignition key in the car connected and locked with other key. I couldn't take the risk as I need the car to goto work tomorrow.
Do I need to replace tumbler or whole assembly, or is my key bad? how can I even tell that tumbler is original and get new keys from dealer?
Please forgive me for asking so many questions, I am trying to figure out all the problems and see what all I can buy and give to mechanic and save some money.

Is it cheap to buy stuff here, auto...hz.,merce.....,o reilly from your experience.

Please see right now, I would have no clue to see what part is called.
Thank you,

Dracs

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1983 300D turbo diesel