Mass Air Flow (MAF) faulty code

[Foxx]

It's for my E46 (2001 3-series), but I know this applies to all bimmers. I hope someone can help.

I have a code P0102 coming up, which is MAF or Volume Air Flow.
At the shop they told me to replace the whole box, but is that really necessary if there is a possibility to maybe clean it, check the wires, replace the sensor or the air intake boot/path?
Questions:
- Where is the MAF located?
- Where is its sensor? can the sensor be purchased at a reg parts store or is it an OEM part only?
- How do I check for leaks near the sensor?
- What's the voltage supposed to be of the MAF sensor? so I can check if it's what it should be currently.
- If I purchase the part, is it fairly easy to replace it myself or do I need a mechanic to do it?

Thanks for all the input.