Which coil?

Following from Rob's link about ignition units . . . . .

I wouldn't mind having a spare coil in stock for my R100GS, as I assume it still has the original fitted and it will go sooner or later.

I seem to remember reading somewhere that they are best replaced with a coil from a later / different model? Can anyone tell me what the idea behind that is, and what's recommended?

Thanks,
Graham W

K series I believe Steptoe said. Or you could contact Mick Barr in Leicester and buy one of his Microlight coils for £35.

The toublesome one is the grey moulded one...it always ends up cracking.

Apart from the cheaper alternatives,the later Airhead one is fine....even though it looks like something off Flash Gordon,circa 1932