Term or phrase for something that changes one's life (for the better) dramatically

Boon

Something that is very helpful and improves the quality of life.

--Cambridge Dictionary

You could modify it with a word such as tremendous, or major to stress the tremendous and dramatic impact of the boon.

Behind this flawed creation of technology, however, was hiding an epochal momentum of my life.

Your sentence is a little awkward (epochal momentum, aside), I would rewrite like so:

Behind this flawed creation of technology, however, was what was to become a major boon for my life.

Philosopher's stone gets you closer at least.

More the experience of something than the thing itself, but epiphany comes close, I think. For example, the firm Epihany A.G. states on its website:

An experience of sudden enlightenment, a positive feeling, a scientific or economic breakthrough which allows a problem or situation to be understood from a deeper or new perspective. This is an epiphany.