I love researching this sort of stuff, learning more about electronics. I purchased both polypropolene caps as mentioned, and the PSU works a treat. During this process I also replaced the 10V 220 uF capacitor near the heatsink that apparently is a common weak point, even though it looked fine. The old paper caps were cracked and split in several places, when they fail they reportedly give off a terrible smell that lingers for days - thankfully I didn't have the Apple II on for long to work out something was wrong.