Perhaps the sales literature was referring to an oil cooler leak that could be isolated with the bypass switch, thus allowing continued operation for at least 30 minutes. A previous post indicated that two and a half hours had elapsed on the test machine, which obviously was not a FAR29 category "A" test. Hence no mention in the FAA TCDS...I'm quite sure that no pilot worth his salt would ever put too much faith in a manufacturer's sales pitch.
From what I've read in previous posts the RFM states land immediately on MGB pressure < 5 psi and that's what should have happened had the guys had enough time to execute that manouvere. I suspect that the MGB temp went to ambient when the guys were dropping to 800 feet as there was no lube oil to wet the sensor, they checked with flight ops and they said "probably a faulty MGB press sensor, bring it back to the hangar", the guys went to 133 knots and didn't know anything else was amiss until the pressure went to zero and the MBG failed along with the inputs for the AC gens, with not enough time to active the APU and/or arm the flotation bags (couldn't happen anyway as they were > 80 knots) hence the FDR/CVR switching off and the flotation bags not being released on water contact. This is only supposition but I can see how this hypothetical sequence of events would make sense.
Robert Decker, the sole survivor of flight 491, is now recuperating at home, and will hopefully shed some light into the actual events of the last few fatal minutes. I'm sure the TSB will glean more data from the remaining avionics components that are still being analysed by the specialists.