Measuring the size and winding of the original one, inductance calculators gave an estimate of about 300μH, which is reasonably close to 330μH that it probably was.According to the datasheet, for 12V input, 5V output at 0.45A, I should be using a 470μH inductor. So I dug through my junk pile, found a T106 size iron powder core that was green with one side blue, meaning it has a permiability of 75 and is good to about 1MHz.
"Ring core calculator" (freeware program) said I need 70 turns (243cm of wire), couldn't find what wire I should use, so I just grabbed the first reel I came across, 0.255mm diameter which should be sufficient. Half an hour of winding later, I had in inductor that replaced the original one, only downside is that it weighs 36g instead of the 27g of the original one...the core is ridiculously large for such low current, but I don't have anything smaller that can fit enough turns for 470μH.
It's quite interesting that with switchmode regulators, drawing less current means you need more inductance to function properly, and vice versa for larger currents, where the core size is predominately dictated by wire thickness, as you need just a couple of turns. (but you have to be able to physically stuff it in/on the core)
For 5V out... © ON Semiconductor
TL:DR - input power is now 2,81W (instead of 3W), making n=76,6%, so - yeah, improvement, but nothing to receive a prize for...