This Model 1 Terramite is from between 1965 to 1972....cant find a good picture of it online....
Main relief is not in the picture when outrigger cylinder is bleeding down. Control valve in neutral makes work ports closed.
If piston seal is leaking and capped side holds the load, cylinder rod is retracting and that rod volume of oil must be displaced through the control valve, if there is no external rod seal leakage. Only an eventual work port relief, or spool could leak. If piston seal is leaking, pressure will equalize on both sides of piston.
Bleed down in one minute do not tell the entire story...diameter size of rod and how long retract will determine leakage volume....
OP should also make sure this old control valve really sets in the real neutral position, maybe it is sticking a bit and not closing the work port properly...spool stiction from rust etc could cause bleed down too....if spool is 1/32-2/32" off from neutral could be enough....