When you have your cylinders refilled (tanks are in MHs) do they both take at least 7 gallons?
When refilling your cylinders is the place that refills using a scale? (BEST Method ----most accurate)
By opening the 'bleeder' valve? (Second best.....liquid spews when cylinder is filled)
By waiting until OPD shut-off filling? (Least desirable method due reliance on a float)
By measured gallon? (Worst method cause it is not temp compensated)
Relief valve on cylinder could be weeping
OPD threads could be leaking
OPD bleeder valve could be leaking
Crimped connection on pigtail hose could be leaking
A little time/effort checking for leaks using soapy water could find the culprit
(Rinse soapy residue off thoroughly after checking)