Thanks for all the helps.
@DmitryL, I use 2 cap in series so each bears 1/2 of the voltage in the circuit. The original cap is labelled 1.25kV, so 1/2 of it is 625V which is within the 630V of the replacement. But current leakage is what out of my knowledge.
@edavid, I suspect C3 because of this article
http://www.pavouk.org/hw/lamp/en_index.html said most likely failure is C3.
@SeanB, the lamp should be fine since it's new and I tested it before I buy. If R6 open, there shouldn't be any startup blink. Will measure it tonight to confirm when I return home. From what I observed (see my first post) the tube can startup and cannot sustain, so I suspect it's the resonant circuit C3, C6, L1, TR1(1-4). For Q1, I measured the resistance of each leg and is the same as Q2. So I guess it is fine.