Yup, while most of our guys have some hands on experience with the ND, Steve's the only support tech who has been totally immersed in them - he and I are the only two left who worked on them in Final Test... him in Bangor, me in Halifax. Lots of good suggestions here and you've got good ideas. As a rule, if there are repeated failures, something is awry somewhere. My initial inclination is usually to look for a cracked cap in the combiner (rear of the filter cabinet). That will impact tuning, stress PAs and could lead to output network failures... plus, depending on failure mode, it may or may not trip the RF Current alarm.
Sorry for the delayed response - 2020 was a crazy busy year and I've just now gotten to where I'm able to catch up all the support sites.