He was guided by a perfect being.

Err, not exactly. Angels are merely avatars of a perfect being, but the only true perfect being is the Allah. Regardless of what the Qur'On says, an angel cannot possibly be perfect. Yes, it is a plot hole. We are talking about documents written 1,500 years ago. It is simple anthropology that literature of that era was very scattered.

Had Muhammad memorised wrongly surely the perfect angel would correct him.

But the angel didn't correct him. Neither did the angels correct the messages of Mosis, or Jesus. They just sent another prophet hundreds of years later.

It is very clear from the literature that God is not concerned with granting humanity the perfect end-all of revelation, but rather adapts his message to the human society at that time.

In other words, none of the prophets are perfect. They simply adapt a message based on the society, and each prophet thinks they are restoring the purity of message.

Food for thought: Why would Mohammad be the last prophet? Is God almighty really binded by his words? We are talking about the creator of the universe here. If God ever wanted to send another prophet, he could. And that message will be adapted to the society of that time.

Thousands of people memorised the quran in the beginning.

Which results in the broken telephone phenomena. You know, like that game kids play in kindergarten where they tell each other a story in a circle, and how the story gets distorted. This is psychology 101.

Muslim scholars do believe that it is the literal word of god

Those people are also pretty pretentious if they honestly think the creator of the universe would limit his message to the words of a single book. Again, again, again, we are talking about the creator of all existence here. Is the Allah restricted by the promises of human concepts such as words? Such arrogant assumption and disrespect to the Alpha-Omega is very un-Muslim in my opinion.

Look, what is even more evidence of God's word than a book is the world we can see and touch around us. This world is governed by the laws of physics set by God himself, and we humans are a result of his design. Because this world we stand on and feel is a direct account by humans of all cultures, it is there for superior to one man's account of the world.

Here is some extra food for thought: Because Allah adapts his message to the society at the time, what if physicists, who study the most direct evidence to God's Law, are the prophets of our time?

If God is real, then his existence needn't be a broad spiritual concept. It is something we can see and feel, like the ground we stand on, and like the atoms we study. It is naive to think that which we learn today is irrelevant just because it contradicts one man's account of the Qur'On.