Scott Dorsey actually said:

Thirdly, if he didn't know any of these things, it should have taken him
less than five minutes to find the leak with a can of starting fluid. There
is ABSOLUTELY NO EXCUSE for someone to bring out the smoke machine for that
sort of leak unless they are trying really hard to find ways to bill their
customers for something.

This is dead wrong.
Everyone knows that hack.
It doesn't work for the E39.
It might have worked for 1970's era cars, but not the E39.
There just isn't any change in the engine speed no matter where or how or
what you spray on the underside of the plenum.
The leak is just too slight and the difference in engine speed too slight
and the chance of getting the fuel from the plenum to the plugs too slight.