If it's intermittent, I'd guess that it's the brushed getting short - they won't always get a good contact. Or do you mean they glow when the car is off? Then it's the diodes
14.6V is a bit high - I'd be worried about overcharging your battery at that voltage. It shouldn't do much more than shorten the life of your battery, but a modern alternator will sit at around 14V.
My old 18ACR? put out 14.5, and it was playing up a little, so I swapped it out for one of convertable mini's alternators (he's a member here) and it's been working fine since. If you're reading 14.6V, and your diodes need replacing, I'd just get a upgraded alternator with a good transistor regulator (read: any newer alternator).
If you do want to re-do yours, you can solder new diodes in yourself cheaply and easily, but the regulator is non-serviceable, and you may need to get a new one.