Doesn't $999.50 buy you at least some "why" behind the "knowing where to tap"? Some tips on diagnostics, some idea why tapping at that spot resolves the issue? Seems like pretty steep price to pay, if you are left without any recourse when the thing stops working. What do you do, call the engineer again, pay the $1000 again, never getting any wiser?
btw, is the price adjusted for inflation? $1000 seems were going rate 1977 - https://quoteinvestigator.com/2017/03/06/tap/