2004 Audi S4 P0300 Misfire & Lean Fuel Trim Codes: Coil, Injector or Electrical Fault?

I own a 2004 Audi S4 (V8, 4.2L) with 94,000 miles and am experiencing sudden, severe misfire issues accompanied by a blinking check engine light. I drove approximately 2 miles home under these conditions before returning to read the fault codes. The only detected error codes are P030-0 (random/multiple cylinder misfire) and four associated misfire codes affecting all pistons on Bank 1. Given that this issue developed recently, it is unlikely a new code would have been generated yet — suggesting an ongoing or developing problem. I suspect one or more spark coil failures, especially since the spark plugs are relatively recent replacements. Two puzzling fuel trim readings have emerged: - Short-term fuel trim on both banks is flatlining at zero — no variation observed. - Long-term fuel trim for Bank 1 exceeds 12%, indicating a lean condition. - Long-term fuel trim for Bank 2 is around 6.4%, also showing significant lean. My primary question: Why does the short-term fuel trim show zero (flatline) on both banks when long-term readings clearly indicate lean mixtures? Background: - Previously replaced the PCV valve with an aftermarket unit, which now buzzes loudly during engine operation. The noise stops when I press it forward toward the cylinder head — indicating suction is being created at the oil cap, confirming proper function. A new OEM PCV valve has been ordered. - Bank 2 EGR valve was in good condition in September; however, I was unable to remove the Bank 1 EGR valve due to a tight bolt requiring specialized tools or engine removal. - The MAF sensor has been cleaned twice — though advised by a local technician that excessive spray can damage it. I only sprayed along the wire and have now ordered a new OEM MAF sensor. Secondary question: Among these potential causes for Bank 1 misfires, are there other possibilities? 1. Leaking fuel injectors on Bank 1 — I removed all injectors but cleaned only one; replaced O-rings and pintles on that single injector. This was a poor approach. 2. Vacuum leak affecting only Bank 1 — no visible leaks found; however, the lean readings suggest possible vacuum issues impacting both sides, making the misfire codes on one side confusing. 3. Camshaft tensioner or plastic bracket failure (based on an Audi forum post). 4. Electrical fault specific to Bank 1. 5. EGR valve on Bank 1 — still inaccessible for inspection. 6. All four Bank 1 spark coils failing gradually, with one eventually blowing completely. Any insights into these issues or alternative diagnostics would be greatly appreciated.