Z3 Roadster (E36/7) M54 trouble code reading (po300)

Firstly, thanks to all for their words of wisdom. Having invested in a DTC reader - what a brilliant tool ! - I now know that the reason for the EML and limp mode on every journey (when pushing past 4,300 rpm) is due to a 'random/multiple cylinder misfire', code PO300.
I have two sets of freeze frame data, which although not identical, make interesting reading. Trouble is, I'm not knowledgeable enough to know what it all signifies. (I also have six different 'manufacturer control' codes - although I imagine that's normal.)
At least the problem appears to be consistent and isn't particularly related to the engine warm-up cycle.
So far, I've changed oil, plugs, air filter, fuel filter/regulator, MAF sensor and the DISA valve. I don't think it's a dodgy coil-pack because the misfire seems to be 'random'. At 87,000 miles could the Vanos seals be acting up ? Or is it more likely to be caused by an air leak somewhere in the intake, cam cover, or manifold systems ?
I tend not to think that the EGR crankcase vent valve is stuck open, because the car idles perfectly around 700 rpm. It also seemed to pass Raj's lunchbag test (!) and I could hear bubbling in the oil pan when I blew hard down the top hose. Although I love this Z dearly, It's beginning to drive me nuts ! Ideas anyone - PLEASE !!
(Latest freeze-frame data as follows ;-
LOAD 16.1 %
ETC o F 185
SHORT FT1 3.1
LONG FT1 3.1
SHORT FT2 7.0
LONG FT2 -0.8
RPM 4335
VSS (MPH) 92

Cheers & Merry Xmas!

Hi to all BimmerFesterers - especially those with Z-Sleds ! Just wanted to post an update on my recent engine management problem (to do with the emission control system), just in case it helps someone in future. Although my fingers are well & truly crossed, I'm now confident that I've discovered the reason and fixed it ! These straight sixes are wonderful engines, but elderly management systems are clearly susceptible to poor sealing and air leakage. The 'O' ringed joint between the main air bleed hose and the top of the cam box cover at the front of the engine (held by plastic clip) was weak enough to allow an intake pressure differential in the manifold (yup, I'm guessing!) I can now run the motor to the redline without triggering a shutdown response - and she goes like a rocket ! It just shows how simple, and often, dumb things can unfairly label great cars and engines. Cheerio & keep the faith!