I bought a Tektronix 453 scope for exactly the reasons you describe. It's the last scope they made that doesn't use proprietary and discontinued IC's.

That instrument shipped with a schematic, BOM, and theory of operations. The theory of opps is a very interesting document. The scope is filled with interesting and useful circuits. It's the ultimate in discrete analog circuitry.

I'm sure I don't have the expertise to really fix the thing and it's sort of useless but it's still really cool and perhaps some day I can learn something from it. That was the point of getting it.