Yep, it can do - a leak is a leak, after all. But the A/G transition is where the body octave key switches to the crook key (or just below the crook on modern baris) - so it's always a prime suspect where A/G is concerned. In any event you'd be wise to rule it out before delving deeper.
A lot of those 'copy' mechs can be very tempermental when it comes to buffering...and something as simple as a missing piece of cork/felt under the thumb key can be a cause of such problems.