I would also check the orientation of the drain/fill port on the bags. A bad impeller won’t pull vacuum and will allow slippage of air and cavitation in the impeller body. The slow leak from the drain indicates water slipping past the impeller. If the drain port on the bag is lower than the impeller body, or if there are any dramatic bends in tubing, your bags won’t drain with a bad impeller.
If you run in heavily turbid or sedimented water, the rate of impeller failure is greater. With the way autowake works, if you surf regular, or port side, your port side pumps may be working harder or running more often to maintain roll.
Only other consideration is if someone altered the ballast system to piggyback PNP bags or additional bags causing a distribution problem.
2020 SA 450 in my future? We will see
2017 Sanger V215sx. We call it Viagra because it's the little blue boat that gets everyone up (For Sale)