The first sentence is correct. Here is a rephrasing: i. The machine was so flawless that (as a result) I could not find any problem even after four hours of probing
The second sentence would be correct if you strike out "such" ii. The machine was a flawless one as (because, due to the fact that) I could not find any problem even after four hours of probing.
Here are some related patterns: so(adjective) that (a consequence of the thing described because of the adjective)
That mountain is so high that no one has ever climbed to the top. The current in the river is so fast that we don't need to paddle our boat, we just need to steer it. The race car was so fast