Even if you switch off your power at the wall, I believe it only switches off live (could be neutral - I can never remember). Thus, as long as the Crack is plugged in you run the risk of being shocked. The only way to avoid that risk is to a) unplug the Crack completely, b) switch the power off at the circuit breaker or c) don't touch any exposed wires when touching the Crack "down under". The shock you experience would not have been capacitors discharging nor would it have been from the tubes. When you touched the exposed wires, you simply grounded the electricity coming in from the wall and got shocked.
Not sure why only one channel worked after that incident. I have been shocked the same way you were once or twice and I have been shocked once from the caps discharging when I touched them immediately after unplugging the power from the wall. My Crack worked fine thereafter although it took me some time to recover - it was less than 3 months though ;). I am assuming you have a bad solder joint somewhere that is now making proper contact again.
It's such a freaky feeling >.<
Anyway now there is constant hiss more on the left channel than the right, i have a feeling it may be dust and or that bad solder joint, or maybe tubes? Ugh wish i was in the US would just send it back to bottlehead to redo it for me, lol