old parts question

[Axle]

I keep servicable old parts. Either to use as a sub-part source, or if working a quick onthespot replacement. If I'm using it for parts, I keep the bad parts to reassemble into a core, such as an alternator, for future use if I need to buy something.
Doesn't cost me anything to keep it, but a core charge is money out of my pocket.

For fuel tanks, I look for one when I need it, my current fuel tank was acquired from someone, who had it for an unknown length of time.