I picked up a 93 525i a few weeks ago and would like the following information.

1: Can i use 0w-20 oil? I use it in my other cars and it is smoother, better gas mileage, power etc...

2: I bought a Dinan Chip and installed it but a CEL came up. 1231 which denotes an overvoltage issue and i cannot understand why the chip would cause this. which brings me to #3

3: How does one clear ecu codes in an E34? Do i absolutely need a proprietary tool or is there a manual way to do it?

4: headers: Worth it or not?

5: Pixels on dash computer are going haywire then blank out, is there a way to simply disable the LCD readout?

6: I have the Blautpunk Business CD, is there a direct fit subwoofer that will fit in the center rear fold down arm rest like I see in newer 328's?

7: I am changing the oil today, can i clear the oil service meter manually>?