See, whenever I have the rare Lucas flare-up, it can be traced to poor maintenance...usually, its a corroded connector or ground...occasssionally, an instrument will finally - after 30 years - fail....but, Lucas problems? No, not on a properly maintained car....& I 'll bet the horn system just like everything else was over-designed at the factory.
Remember, I'm the guy who took off across the US, Canada, & Alaska in my RV on a 15,000, 6-month trip with only my '79 MGB for daily transportation....true, I'm its only owner & have done all my maintenance on it religiously.....the only thing that failed was the OE air pump that I forgot to do maintenance on before we left...I'm still convinced that, had I sprayed white lithium grease up inside it before we left, it would still be working!
I'm not gonna worry about my horns.