That's assuming that input signal is always the same or similar. It normally isn't.
Volume pot only attenuates (and may affect the loudness circuit, if it has a loudness tap), so whatever ALWAYS happens around 3 or 6 on the dial regardless of the input signal level, the reason is probably the pot itself. To test it properly, best to try first with a loud source (like built in FM tuner, or a CD player), and then connect a weaker source, like an mp3 player with volume at 30% or lower and try again. If in both scenarios the right channel comes in at the same volume pot position, and then balances out at the same position - not a voltage issue.
I would still bet on the volume pot, with this kind of behavior it's very often the cause. And I've found reports of volume and balance pots going bad in SA-202.
Drucifer83, if my search is correct, for your Technics you need a 250 kOhm logarithmic pot with 'D shaft'. If you can't find one exactly like that, maybe just get something with a different shaft and change the volume knob. Make sure that if physically fits in the space it will be in.
Don't bother looking for it with the Panasonic part number, this exact pot is not available anymore.
If you can't find a volume pot that physically fits, there is a workaround. You can buy or make an inline variable attenuator and put it in the tape loop. If you want to buy, they are quite cheap, 7-12 bucks will get you one. Search for "CALRAD 10-105" or "Rca Level Controller" to see some examples.
If you want to build one, buy any stereo volume pot (logarithmic/audio taper is better), and solder RCA wires to it.
Then plug the thing in the tape loop, put TAPE MONITOR switch to TAPE position (and best block it in that position with something). Then set the added pot to the position, at which your normal listening level is at 7 on the Technics' volume pot. It's far from ideal, but at least it will give you balanced sound at your normal listening level.