The exact name of the original transistors is 2SC2307 but they just printed C2307 on the case. This is a typical code for japanese transistors where C means NPN transistor. So the NTE2308 is a NPN as well and if I remember right specs are very similar to the 2SC2307.
Donīt know where you are living but if your mains voltage is in the 110V range these could work. For 230-240V mains voltage these are not good enough, I used different ones rated for 800-1000V.
Just didnīt find my repair notes until now. Anyway you should replace both of the highvoltage transistors even when only one seems shorted. The powerdiode near the transistors usually is OK but you should check.
Sometimes the bridge rectifier at the voltage input is shorted too, you should check again. Regarding the other diodes which are used in the area driving the power transistors, some of them are shorted usually always. You should replace all of them.
Donīt know your degree of electronic knowledge, but a word of warning here. The voltage generated in some area of the powersupply is very dangerous, please be carefully here. You should remove the powerwire (mains voltage) always and deadshort the big capacitators using an isolated tool or wire before working on the unit.