Panasonic CT-1310M keeps blowing horizontal output transistor

[ARC Tech-109]

That weird white substance is the silicone heat conducting grease and without it the transistor could fail from overheating. Same stuff used on processor heat sinks and should always be used. The tape itself is not very heat conducting and its breakdown of 600V is the MAX at its nominal thickness not compressed under a transistor. There can be upwards of 1000V between the transistor case and ground during the flyback period and this is why it is so important to do things the right way, HOT's are not cheap as I remember and so far I've seen about half a dozen blown in this thread.