My boat's interiors are also 100% teak, all in good condition except for the pilothouse, which is subjected to the most wear and UV exposure. I stripped all varnished finishes in the pilothouse down to bare teak with a hot air gun, and recoated with urethane varnish.
My goal was to match the orginal finish of the other cabins, so obtained the original spec from Nauticat in Finland. A wood grain filler paste was first used to fill all minor cracks and open grain - followed by sanding after drying. Then four coats of Interlux Goldspar satin, fine sanded between coats - finished the work. wood grain filler
It looks great and resulted in a glass smooth surface, free of voids - which would otherwise detract from the finish. If your cracks and gaps are fairly large, try applying the paste in layers, drying between each. A teak tinted stain could be used to darken the filled areas, using a fine brush, to obtain the desired effect.