We all make jokes about Lucas, including me, but Trevor is right. With some basic maintenance they will perform perfectly and give years of trouble free service.
It always amazes me to read that someone has just spent £2,500 or similar on a engine rebuild by SRM or someone else and then have trouble getting it to run properly because they put their 60 year old magneto back on.
When it comes to old bikes the magneto is the single most important item on the bike. I always look at it like this...
If the engine is worn it might use oil, blow smoke, rattle etc, but it will run and get you home.
If the carby is worn it might run rich, or lean, not idle properly etc, but it will run and get you home.
If the magneto is had it then it wont run and you will have to walk home.
I had a magneto fail on me about 20 years ago, the coil melted and glued itself inside the body, since then I have always reconditioned the magneto as soon as I get the bike. Even if the bike comes with receipts saying the magneto has just been done I still get it rewound with a new condensor.
A good example of that was when I bought my '55 B33 a couple of years ago. It came with receipts for a magneto overhaul including receipts for a new condensor. I pulled the magneto apart and the coil was like a sponge, soft and starting to fall apart. Whoever had "overhauled" the magneto had replaced the condensor but thats all, the rest was shot.
Which brings me to my next point, when you do get your magneto reconditioned send it to someone with a good reputation who guarantees their work. Do not give it to your "mate" who has a "friend" who "does up" magneto's.
Sorry for the rant but I get sick of seeing people at rallies pushing bikes up and down the road to get them going when you know that with a good magneto they will start easily. All my bikes have good magneto's on them and they all start first or second kick hot cold or anywhere in between.