Very ancient, very replenished D76d, made up on the 3rd May 1985 and kept going ever since - But kept going carefully with test patches at zone VIII and XI to make sure everything is going well every week or so
I use the alternative replenishment method whereby a fair bit of fresh D76d is used with the D76d replenisher - 70ml of replenisher to 80 inches square each (a sheet of 10x8", 4/5x4 or 1/120 or 1/36-35mm) of mix instead of just the 28ml of D76dR - (See "76 Years of D76, Ryuji Suzuki, Silvergrain.org)
I use a narrow measuring cylinder with a piece of tape glued to it with the number of films to be replenished marked up the tape, for three sheets I top up the the third line and so on
Recently I bought a step wedge via APUG to calibrate a densitometer I had been given - This gives me much greater information on the state of the developer, a crucial thing when using old replenished dev' - Replenished dev' has to do a lot of work it to keep it young and healthy, like all us