Service on Marantz 10 b

I have a Marantz 10b that needs service. I live in Mich and would like to know who are the best service centers for this old but beloved tuner. Thank you for your help.
What kind of problem does it have?
The 10B needs no routine alignments of any kind. The photocells do fail on these and that's the most common ailment.
If tubes test ok and unit works in stereo with muting action, I would just enjoy the unit.
But if you MUST send it to somebody, I believe there are three repair facilities that are considered the best:

In order of preference:

1- Terry de Wick in Knoxville Tenn.

2- Mike Zucarro in San Diego

3- Audio Classics in New York
Thank you. One channel has a random lowering of volumn. All tubes test good.