Amazon: Damaged JFUR4 distributor

[HRA]

I've got an Amazon saloon with a B20A engine. A while ago I set-up the ignition timing "according to the book" - 19 degrees BTDC at 1500rpm with the vacuum disconnected and plugged. The car ran well and felt lively enough but there was obvious pinking on acceleration in top gear up-hill. So I did the usual thing and backed-off the advance at the distributor. Things got a bit better, but still some pinking on acceleration up-hill. So I backed-off the timing a bit more, but the pinking is still there. OK, so I'm not heavy-footed and I don't often notice the pinking, but with the timing backed of some 10 degrees now the car isn't so lively.

Last night I finally got around to looking at the distributor. I wondered if there might be a problem with the centrifugal advance, and indeed there was. The mechanism is quite free and the light spring is fine. However, the heavy spring had become detached at the outboard end. On closer inspection it looks like the top of the attachment-point has broken off. This is a finger of sheet metal that should be wide at the top, thinner in the middle, then wide again. It looks like it has snapped off at the thin section.

A few minutes with a couple of files and I've managed to refashion the remains of the finger so I can get the spring back on. It feels reasonably-firmly attached but it is only a running-repair. I've managed it so that there is still some slack at the other end of the spring where it mounts on the round post, so all should be reasonably good when I set the timing-up over the weekend.

I'm going to look-out for a second-hand distributor - perhaps one that is going "for spares". Is this wise or is the damage I've seen a common failure mode? Is it worth a gamble on an old unit or do they all break in exactly the same way? Any advice would be much appreciated!