so my bass tech removed and reinstalled the electronics from my 1994 europa (which was sent into alembic for some work). i went to pick it up last night, and he tells me he couldn't get the high-pass knob back on. that it's a friction attachment (not pin), and he worked for hours on it and can't figure out why it won't slip back on. any advice? is there some trick? he was adamant not to use a hammer for risk of damaging the pot.