It is a pair of books by Michael Kring. The Space Mavericks (1980) is the first book, the second is called Children of the Night (1981).
Here’s the blurb for the first book:
Transporting valuable cargo between opposing galaxies. Fripp and Kahn ran afoul of interplanetary law, and found themselves playing cops and robbers as they shuttled desperately from one lost world to another, pursued by the space fleet of the vengeful police! Their only chance for survival lay on a desolate planet whose inhabitants had mysteriously disappeared, leaving behind traces of an advanced civilization – and the secret of regeneration, for anyone bold and clever enough to decipher it!
and the second:
A Subterranean race, a powerful dictatorship, an ancient space ship embalmed in coat. All these and more await space mavericks Fripp Enos and Kohn Tarkosz on the planet Vespers, as they continue their search fr the source of Fripp's magic ring.
The blurbs, along with the covers, can be found on Fantastic Fiction. I've not been able to find anything on Wikipedia or an author website. Seems these were the only two books the author ever wrote.
I put the same answer here for this question