I completely understand. It's been a roller coaster ride.

If you have the energy and time while awaiting arrival of the new solenoid, it may be worthwhile testing the engine vacuum pump using the gauge on the handheld pump. This would be done by disconnecting the small turbo hose at the engine vacuum pump and then connecting the handheld pump to the free small nipple. With the engine idling, the vacuum reading should be a steady 25-30 inHg.

 

The engine vacuum pump was both recently replaced, and also I have already tested the vacuum while idling by T’ing off while doing a wastegate test at idle.

I also spent the last few hours removing the known good boost solenoid from the other MINI, putting it in mine, and testing it, same fluttering issue, but my wastegate actuating test was successful, so now I’m really lost… it’s almost like the boost solenoid is bad, and something else at the same time… I am still ordering a nice boost solenoid from ECSTuning and going to put it in, but at this point unless something else comes up the plan is to bring it to put the new boost solenoid in, probably won’t fix the issue, and then bring the car to a shop. I’m just at a loss
that 0.000001% chance struck, and it struck hard :(

 

Is it time to return to the Wagner intercooler taken from the 08 MCS? Is this the same 08 MCS that had a similar problem as your 09 MCS? A bad intercooler could cause a boost leak.

Does your car have a stock N14 ECU or is it tuned (required for cat-less exhaust system)?