Guys, maybe you're not used to reading technical drawings? The picture at the top is the entire venturi assembly. Below it are 2 half sections through the wall of the venturi at the location of the bore for the air injection. The other half is not shown as it is of no consequence. The air is sucked in through the grommet, takes a right angle turn into the bored hole and is delivered to the needle-wheel cavity of the pump. The principle of the venturi is that a low pressure is created in the needle-wheel cavity which sucks the air in as the water expands from the inlet tube into the needle-wheel cavity. It is therefore paramount to deliver the air to the low pressure needle-wheel cavity.
The potential problem that the manufacturer has identified is that the bore or shaft that delivers air to the needle-wheel cavity may have breached the wall of the tube where the incoming air is turned at right angles. This can cause either water to be sucked into the venturi air bore instead of air from outside or air to be sucked into the water tube. The result is less air being chopped up by the venturi.
Don't drill your air hole straight through or you will loose a big chunk of performance.
I have examined my venturi and found it to be intact - no pin hole. That's good, so what are the alternatives? Well, the only way inwhich performance can be lost is if air is being sucked in from other joint areas -- notably the union joints! Or, if there's an obstruction.
Scubaduderon discovered the venturi grommet protrudes into the bore for the venturi and has drilled it out. You only need to insert a drill bit of the correct diameter and turn it with your fingers; you don't need to use an electric drill -- just turn the bit with your fingers to remove the unwanted end of the grommet. Then clean it out by blowing into the grommet end of the hole.
Next, to ensure that air is only sucked in through the venturi, I have put a couple of turns of teflon tape around the threads that connect to the pump intake and the union at the opposite end. That will seal and prevent any air being sucked in through the threads.
Finally, I took the spare black washer that came with the skimmer and placed it over the washer that was cut to prevent obscuring the air passage into the needle-wheel cavity. I did this to safe guard against the 'cut' washer deforming when the assembly is tightened up.
The results? I can't be 100% certain, but these are my observations:
(1) The sucking noises around the unions has stopped;
(2) There appears to be better bubble density;
(3) The skimmate foam texture looks more like my beckett skimmate foam texture;
(4) The air-pump is no longer able to augment the air -intake.
Tone
