Yes i had a problem with my ML 431 which i owned for 5 years , it could easily have been rissen because i had a melted head fuse (not correctly placed by the electricity company) which gave me serious voltage fluctuations .
The dutch importer / Mark levinson handled it professionally and replaced a complete section with a new one (guarantee period), besides from that it was absolutely fussfree and a pleasure to operate and i still mis those fronts and red standby lights , just look inside one , the build quality is formidable , i only heard of the earlier 3 series that they sometimes had to have their powersupply caps renewed.
I will probably buy back some 436 amps one day, to me it is still the /one of the nicest SS i ve heard ,despite all the newcomers on the market