I may be talking to myself or no one but maybe someone will have the same problem as I had replacing the mercury cell inside this meter.
My solution is a Saft LS14500 sealed primary cell with 10 years shelf life and 2600mAh capacity, followed by a TPS709135 ldo with 1µA Iq. Mounted on adapter pcb with some capacitors.
There is some very small amount of noise visible in the 0.001 range multiplier setting, but totally acceptable and now this meter is finally fully restored.