zynmb

I'm a newbie. I just bought a ML 350 2011 (17000 mileage) from Carmax. I found engine oil was super dirty and had them get it changed. They said they had it changed in Jan but used normal oil instead of synthetic one. That's the reason why it was so dirty. I suppose no one should be doing a long drive in Carmax after they had it. I started not trusting them on what they were supposed to do when delivering cars and what they said. I have a few concerns now.

1. The steering noise. When I steer to the left end or the right end and steer back, I can hear a bit zizi noise. I wonder if there is anything wrong with steering system. What could be the reason?

2. The service interval. My screen showed the next maintenance is after 9000 miles. I wonder what's the computer behavior if the former owner or Carmax missed the last service. Would the computer say overdue or it just passes it and says next service time.

3. Today I got a coolant level warning and found the coolant was 2cm lower than the mark. What coolant do you buy? Do you buy it from a dealer? I dare not ask Carmax to do it as I suspect they may add a strange one to mix my coolant.

4. Washer fluid is also low. What do you suggest for that?

5. The brake fluid level is ok but I'm not sure if it needs to be changed too

6. How do I check steering fluid?

I know I have too many questions. I should probably have it professionally checked by a dealer. I'll do if necessory. But I really want to know your advices before I throw money on it.

You don't have to answer all. If you have an idea on one of them, please just enlighten me on that one specifically.

Thanks a lot Guys