Speaking to an engineer from Malaysia, some engineers use soap and water, instead of the approved leak detector fluid for the oxygen bottle leak test. This is a poor maintenance practice.
I agree that using soap and water to detect an oxygen leak is potentially dangerous. That said, what evidence do you have that Malaysia Airlines engineers adopted the practice, or that it was used over a prolonged period on Malaysia Airlines aircraft? Anecdotal evidence that "some engineers" use soap and water in lieu of approved leak detection fluids is hardly evidence that it occurred in the MH370 case.
BTW, the engineer in that video isn't Malaysian, he's not working in Malaysia, and he's not working on a Malaysian aircraft.