Channel Balance question??

[Ograv]

So I buy a vintage Rotel receiver. I hook it up & seem to notice a channel imbalance issue. It seems like the left channel is slightly lower in volume, when listening to it in a near field situation. Far field (>7 feet) it sounds OK, but I still seem to think the left is slightly lower. So I investigate & find that the left channel speaker output is ~15% lower than the right & correctable with the balance pot. I work backward & discover the output from the preamp is 15% lower So the "issue" is in the preamp. I check the HFE all all transistors & all match pretty good, caps check good, check many resistors & those are good. Can't find a problem. Check the volume & balance pots & see some variation there. So for reference, I check 2 other receivers I have (Tandberg & another Rotel) and I find the same thing. Below 10WPC, the right channel is stronger than the left by 10-20% WPC. Is this typical? Anyone else experience this. OK the sample size is not large, but it is bigger than a mass sample of one. Hard to believe that all 3 receivers would exhibit the same channel being "significantly" higher than the other. I tested the channels with a load & without (AC voltage at the speaker terminals) and measured the output voltage with a Fluke 189 & wattage with a Sencore Stereo Tester so I know the measurements are accurate & correlated. Thanx in advance for any responses. - Bob V