Disagree that there's grey areas. AirlinePirate, the following sections are worth a read...
CAR207
CAO 20.18
Aviation Ruling 1/2004
CAO 20.4
CAO 20.11
CAO 20.16.3
CAO 20.18
AIP GEN 1.5
CAR 47
CAR 2
MEL and AFM if appropriate
Also worth speaking to a clued up engineer... the good ones tend to be really good with this sort of stuff, more so than most pilots I've met. They're also aware of the gotchyas in the system. e.g. if NAV2 is broken, removed from the aircraft and we still meet the GEN1.5 radio navaid requirements, we may still be grounded - there needs to be an engineering order applied for the removed navaid (which would generally require the panel to be blanked so cooling of the other electronic devices in the instrument panel are not affected).