I've heard a good number of technicians comment about that design- as I understand it, it is one of Nelson's earlier designs but due to construction or other factors did indeed have a reputation in the service industry (I ran a service shop for 15 years before going into the manufacturing sector) for stability issues.
These days if one has survived I would expect that filter caps should also be serviced out, but there are a lot of amps that are more deserving.
