Even with proper filament control, No Time, there are problems. Something has happened to Econco in the last few years. I was always able to get 12 to 15 months on a rebuilt. Chris Hudak at the CBS FMs is lucky to get 5 months on a tube. And, he is very careful with the filament.
Actually, I would probably buy a Russian Svetlana tube rather than take a chance on a rebuilt. At least until they can work out the problems. According to Chris, the filament seems to lose emission rather early.
I agree, a Gates 5 would be a good choice. Transcom has a Harris SX-5 from 1987. I understand that the SX is basically a Gates 5 with alot of computer crap on it.