just because they "Test" as good, doesn't mean that actually are. HOT's run at very high voltage and very high amperage. the tiny voltage a tester uses to test with is not enough to determine if it's good or not.
the only real way to know for sure is to buy a new known good HOT and use that.
the BU #'s are a philips branded part number. the 2SC #'s are universally accepted part numbers.
either part should perform equally well... there are slight differences between the BU and 2SC parts, but whether or not these differences come into play in this circuit, i don't know. i'm not an electronic engineer.
if the schematic spec'd a BU4530AL, i'd try and source a BU4530AL, otherwise if it ran forever with a 2SC5144 and it's cheaper to get than the BU, then i suppose, i'd go with that.
also, i'm not 100% sure, but quite often with these HOT's, the tab must be electrically isolated from the heatsink (silicone pad, insulted screws) if it's arcing it's shorting to the heatsink. there could be a hole or a burr on the HOT that has penetrated the silicone pad and causing it to arc through. when i'm installing a transistor, i'll use a flat block with fine grit sandpaper on it (600 grit) to burnish down the backside of the transistor. not only does it make it flat, but will eliminate any flashing or burrs on the back that might short out. quite often the molded plastic sticks out and causes the metal plate to not sit against the heatsink and dissipate heat properly.