yeah I sort of doubted it would be the problem but I figured you shouldn't leave any stone unturned lol
Surely if the pressure is building up in the booster and letting that off fixes the problem then it has to be at the booster end?
That pretty much leaves swapping out the booster to see what happens. Which is totally gay.
Never tried it myself but maybe some high pressure air blown through the booster? Or even a little squirt of wd40 (probably really bad lol )