As far as I know, Xtol is the only developer that also serves as its own replenisher. For years, I used it that way in Kodak hard rubber tanks and it never went bad. Now I do less film and, for reasons that shouldn't be examined too closely, am using D-23. I'm now working on a liter bottle of D-23 that I've been replenishing since September. So far, so good. BTW, the Anchell and Troop Film Developer's Cookbook has formulas for developers and their replenishers.
Edwal 12 works as its own replenishing solution too. I've kept a batch running for a few years, and it has been a remarkably stable and consistent developer.
Metol, Sodium Sulfite, Paraphenyline Diamine (PPD), and Glycin. Works a charm.
"Often moments come looking for us". - Robert Frank
"Make good art!" - Neil Gaiman
"...the heart and mind are the true lens of the camera". - Yousuf Karsh