Great episode, second season best so far.
At first, I found it strange when Margo pointed to a problem in solid rocket boosters for Buran. In our timeline, the Energia Rocket utilized liquid rocket boosters. However, when I looked closely at the diagrams on the scene that margo check the Buran schematics, I found that the show version of Buran does not utilize the RD-170 engine but a solid rocket fuel engine.
My theory:
In our timeline, the Buran was managed by Valentin Glushko, which developed the Liquid Lox/Kerosene RD-170 engines utilized on the Energia rocket boosters. In the show timeline, Korolev did not die in 66. In fact, he is still alive and is probably the head of the soviet space effort. Glushko and Korolev had differences. I doubt that they would put these aside for the RD-170 to be possible since, without Korolev's death, Glushko would continue developing engines with hypergolic fuels instead of developing Lox/Kerosene engines.
As for solid rocket Engines, Korolev saw them as an excellent safer alternative for military missiles instead of hypergolic rocket Engines. Korolev even started developing the first soviet solid fuel ICBM (RT-2), which Vasily Mishin concluded.
I believe that Korolev's preference for solid fuels in ICBMs, together with the USA space shuttle's early development (this would give more time to the spies of the soviet union), could lead the USSR to opt for solid rocket boosters instead of liquid rocket boosters.
Bonus Theory:
I also believe that the four engines on the show version of the Energia rocket core are not the RD-0120, but in fact, NK-15VM or NK-35 LOx/LH2 engines since the development of the N-1 rocket was continued.