Oil played a part.
In the early 80’s, the US started a “synthetic fuel” project which spooked the Saudies (OPEC). OPEC, in response, upped its production to make syntheic fuel too expensive to make. This crashed the oil price by half and denied the Soviets it’s primary cash source (oil).
Combined with a faultering centralized economy, unenthused work force, and an arms race from the US, the Soviet economy collasped.
So you think it was hard currency deficit?