@caution sent me a potentiometer that I got in yesterday! To install it, I kept the shaft and contacts of the original pot, and the mounting bracket. I just replaced the wafer with the carbon tracks on it. I had to bend the legs to make it straight, and jumper 'pin 1.' I made the jumper with a resistor leg. Took me about 10 minutes, and the radio is now working!
One weird thing I noticed, capacitor 129 and 229 were different values? One was 0.33uf and the other was 0.22uf. I replaced both with two 0.22uf capacitors. I will be interested to see the schematic so that I can know what value was intended for these positions.
I went ahead and replaced several capacitors with replacements that I have on hand. The radio is now working, but it has a large background hiss, so I'm going to rebuild the power supply as well. I plan to purchase a schematic so that I can replace Q303 (the rusty transistor), replace the diodes from the diode bridge, and replace all of the remaining power supply capacitors. I hope that this will not only remove the hiss, but it will make this radio last a long time.
The RX-5050 sounds alright. It doesn't sound near as good as my '69 pioneer receiver combined with my mid 70s rectilinear speakers, but it sounds pretty decent good. It is very loud, and it is quite a bit brighter. I have found that EQing it by boosting the bass and flat lining the treble gives the best tone. If and when I purchase a schematic, I will post it to this thread, so that someone else won't have to pay for the schematic in the future!