Panasonic CT-1310M keeps blowing horizontal output transistor

[ARC Tech-109]

More of what was available in mass quantity for the best price in the day. When I was in broadcast those Panasonic 1310's were a staple in the edit suites and were more forgiving than the Sony to poor sync and other issues but they suffered from cracked solder connections mainly around the CRT socket pins and the row of power resistors in the supply chain. The connections may "look" good but in fact may have a slight hairline crack, this is common with TO-220 devices where the center lead expands more and pushes harder than the others being it's the collector and part of the metal tab, power resistors will dissipate a significant amount of heat through the leads. Any time there is thermal cycling there is going to be mechanical stress and you're dealing with 40-some year old wave soldered connections that were the minimum to make the set work then.
If all is well in the other circuits the counterfeit transistors should work just as well as the original.