P0300 is random missfire, I take this to be random over many cylinders. It looks like that 1,2,3 miss fire often enough to trigger a single cyl missfire code.

What direction does the fuel rail input run? If 4,5,6 get fuel first, 1,2,3 could run lean and missfire. What is the fuel pressure under load? Any recent work on this car? What if the fuel cross over rail is crimped between between the left and right.

Also, is there a dual intake manifold system on this car? Perhaps there is some sort of interaction there.

I know on a 97 C280 M104 SFI ME2.0 ( ME 2.1 ? ) , dropping a cylinder for 15 sec or so will shut the injector of that cyl down until the key is cycled again.