Now that you've mentioned it, I just cleaned my oily engine compartment & parts with undiluted Simple Green. What a remarkable cleaner!

Okay. You mentioned you just have few seconds before the vacuum was lost. Thats a BIG leak. Listen close to these (big leak points):

1) compressor oil seal - listen near to clutch plate
2) crimped rubber hoses - listen near to crimped ends
3) condenser - dismantle the front grille, listen near front of condenser
4) leave the evaporator alone, not yet this time around

OR coat those sites above with lots of soap bubbles and open the BLUE valve. For the compressor you'd need to fully coat around the pulley + clutch.

You need HIGH pressure to make the noise/leak to appear. Engine OFF. Set up your AC manifold gauges as usual using yellow and blue hoses only. INVERT the 30lbs tank. No need to put on weighing scale. Charge by LIQUID. Fully open the tank valve. Next fully open the BLUE valve and listen/look for the leak! Close the BLUE valve and prepare to listen/look at the next site. Open the BLUE valve again and so on.

You'd need ALL that HIGH pressure to make that noise. Don't worry all would be evaporated into gas and leave the system quickly. No damage here. Just some refrigerant loss.

With such a BIG leak (as you've described) I don't think you'll even find the chance to pressurise the system. Be sure to CLOSE back the tank valve when you're done.

Hope this helps,
Amarin.

EDIT: The liquid to gas pressure would be around 100PSI. Its well within the system's tolerance.