Osborne Vixen - Zenith 7" display t-shooting issues

Need some help on this one.. trying to repair the built-in CRT in an Osborne Vixen portable. There's some complexity here, so I'll do my best to be succinct. The unit presented with a vertical line down the screen, and very low voltages on the scan-derived power supplies - the 50V in particular was doing about 18-20V Removed / tested the horiz. opt. transistor (HOT). Neither open nor shorted, but beta measures ~12. Replaced the HOT and scoped the B & C circuits - base drive was +much+ higher (like 10X) level than the output at the collector. So again pulled the HOT and swapped in the only thing I had that +seemed+ it might work: RCA SK9118 (375) - Pt 25W / Vcbo 200V / Vceo 150V / Vebo 6V / Hfe 150 (typ.) Bingo! Display is now bright & crisp, looks great.. but.. the sub. HOT is running way, way hot. Rose to 170F in 2-3 min, and was steadily climbing. And that's in free air, not sealed up in the case. 50V supply came up to 42V.. better, still seems too low. So I think you can see my conundrum, here.. Is the +original+ HOT actually OK, and I'm only masking another problem in the circuit by installing a new part with 10X the gain? Why is the new part running so dang hot - and if the orig. is in fact bad, what killed it, anyway? To make things worse, I can't find +any+ service data or parts list for the display; all I have is a schematic. Nor can I find a datasheet for the original HOT - so I can't tell if it's in or out-of-spec. It's marked "SGS 1070 / 8309". I +think+ the 8309 is for March 1983 but who knows. Any ideas on this one, folks? =)