Another classic 'caught-out' is the Part-Banana; most if not all have seized fuel selectors (low-leverage knobs combined with slack cables) as no-one ever checks the x-feed during run-ups or preflights
Absolutely right. There were three Partenavia's at Essendon a few years back all with malfunctioning fuel cocks. One of the Partenavia's was brought into a hangar to get a seriously bent nosewheel rectified. It had got bogged at Phillip Island but the pilot flew it back with a buggered nosewheel. Included in the numerous defects found by the maintenance people were totally jammed fuel cocks. There was no way the pilots flying that aircraft could have crossfed or turned off the fuel cocks of either engine in case of fire. The engineers estimated it had been flying in that state for several years and in each case the owner's maintenance organisation had ignored this defect during 100 hourly inspections. The fault lay in the fuel selector valves in the wings and it turned out to be a design fault. In UK, this defect was the cause of two passengers drowning when a Partenavia ditched due to fuel exhaustion when the female pilot was unable to summon the strength needed to switch to cross feed.
Actions by this reader stirred CASA into action and an AD was issued requiring all instances of jamming fuel cocks to be reported and regular maintenance inspections were directed. Despite that, memories are short and it's a fair bet that there are Partenavia's currently flying where it is well nigh impossible to actuate the fuel cocks with one hand.