This is a fantastic and often overlooked piece of the Seiko dive heritage, arguably the "Poor Man's 62MAS" (Seiko's first diver)! This stunning Seiko 5 Sports 5126-8130 hails from the pivotal year of 1969, and its designation of "Water 70M PROOF" on the dial marks it as an incredibly rare, early Japanese Domestic Market (JDM) model. The "Proof" text was only used for a very brief period before being changed to "Resist," making this a highly desirable marker for the informed collector!

The watch is a total feast for the eyes, combining the muscular cushion case geometry of a serious tool watch with a high-contrast aesthetic. The unique checkerboard black and silver bezel gives it the iconic "Rally Diver" nickname, linking it aesthetically to the motorsport chronographs of the era. This design choice is audacious and gives the watch immense character, perfectly complemented by that crisp silver sunburst dial and the signature blaze orange sweep seconds hand—a crucial tool-watch feature for high legibility underwater or during timing events.

Powering this vintage beauty is the sophisticated Seiko Caliber 5126, an early Daini (Kameido) automatic movement that runs at $19,800 \text{ VPH}$ and uses a reliable Swiss-style reverser wheel winding system (not the Magic Lever!). While lacking hand-winding, it features a fantastic 23 Jewels and a handy day/date complication with a quick-set function. This watch represents the moment Seiko truly began democratizing the automatic sport watch—it's a massive piece of horological DNA for a surprisingly accessible price.