7E Vacuum Fluctuation at LO Tank

Hi Gents,
This is a relatively new 7E unit experiencing vacuum fluctuations at the LO tank since commissioning, around 1 year ago.
The readings at the tank PT fluctuate between -3 to 3 in of H2O, and we assume this is causing torque converter oil leaks coming out from its shaft (around 1 gal every 24 hrs). This vacuum is stable when the unit is on ratchet, however when closing the compressor bleed valves, opening the inlet heat bleed valves, and generator sync, the vacuum starts fluctuating.
Site team is checking the piping and tank for any air leaks, however they have not found anything yet.
Do you have any clue where else to look for?
Many thanks in advance