OK, right, let's have another look at this.

Yes, the role of Spark and Brain Module do seem to cross paths on what they are actually for, but I believe this is by design.

When a Spark first leaves the Allspark and comes into this reality, it is -- for all intents and purposes -- blank, without any memory or scope to form an individual personality.

The Spark enters a body and integrates with the Laser Core, thus forming its first link to the Brain Module (Core Consciousness).

The Brain Module has within it basic programming, which guides the young Transformer in their early years. The Transformer grows as it experiences the world, and these memories and experiences and interpreted and stored by the Core Consciousness (forming individuality and personality) and are also absorbed by the Spark.

When the Transformer dies, all memories and experiences are already in the Spark, which travels back to the Allspark and adds to the combined knowledge of a billion Transformers that have come before.

The Transformer's body could then be thought of as a hard-drive. If you hooked their body up to a machine, you could browse their Brain Module for information.

I think this is closer to what I'm trying to say, but still haven't put it forward eloquently enough.