DSC and xDrive malfunction

[RICE]

2011 X5 E70 35i
Last Friday, my car did two recalls (airbag & tank) at the local dealer and an oil change. Took 3h and $109.
Last Sunday, 4x4 yellow sign appeared. I only drove about 3 miles last Saturday, it was fine.
Here is the $79 diagnosis the dealer gave: Steering angle sensor-1.25k, Oil filter housing gasket-1.1k and Rear differential pinion seal-0.8k. Total-3.3k
Here is my diagnosis: my car drives fine, rear two tires were small trembling when I turn and brake in low speed. I did the steering wheel trick, that turn full left and full right, 4x4 sign disappeared once, but it lights again in a minute. The trick only worked once. Also, no idea with engine oil leak and seal leak, I mean I haven’t see any liquid.

Should I do another diagnosis? Can these three replacements DIY? I searched the parts, they are cheap.

Lastly, I think this is weird, my car is fine before I went to the dealer. I had another water tank replacement two years ago, it was also after went to a dealer’s recall and oil change.