Have you considered that it may not be a mere transistor failure? IN
other
words, something else went bad, and took the transistors with them. And
if
that's the case, the problem won't go away no matter how many transistors
you put in there. You need to figure out if there is something else
wrong. At least you have the manual.

I went through the output circuits checking for shorts with a the diode
function on a DMM, prior to replacing the transistors. There must be some
kind of fault that won't show up this way, I guess the only solution is to
replace the pre-drivers as well.
I paid about $8 each for the transistors here in Canada, but have since
located a US supplier that sells them for $2 ea. They have a lot of got
prices on semis so may order a bunch of stuff from them. Of course, they
might not be of great quality....
I should have realized the difference with Darlingtons. Why couldn't all
manufacturers just use the same parts, and save us poor techs the trouble
and expense of finding so many different types?