Those 'old farts' in brown overalls were worth their weight in gold!
As a pilot under training, one day when I turned on the battery master in my Jet Provost, the AC inverter didn't respond. Cycling the battery didn't help and the young lad outside hadn't a clue..... So he sensibly went and fetched help.
Out came an elderly chap in a brown coat. He opened up the nose, reached inside and gave something an almighty clout with his fist. I felt the aircraft actually move.
"Try it now!"... Click, whiiiiizzz - and the inverter started up as normal. After I got back from an hour scaring myself over the Bardney sugar beet factory, I spoke to the line chief. It seems the old boy had remembered that trick - he said he hadn't seen it for a few years though; in fact it must have been about 12 years since he'd last seen that particular snag when some even older fart in a brown coat had taught him the trick.
Old age and treachery will always outfox youthful enthusiasm!