Sansui AU - 919 Thrift Store Find

I think it might need output transistors. Also someone mentioned that the AU-717 was similar to the 919 with just more power. Not so. They are both quite different.
Funny about loosing the channel. Hours after I re-started the unit it lost the left channel, and the right was fine. The unit can be ran for hours before it does this. Weird. But not surprising. I mean who dumps a nice working Sansui AU 919 at the local Goodwill.
Although I have been surprised. One of my finds was deleted from the postings on here because I guess it hurts the sellers of these unit on here. And that unit works fine, and is more recent. Early in this decade production
Anyway when the Sansui was running it sounded great! $50 admission, and service fee won't hurt. I am flipping some pieces so I might put the funds towards a service. Or I may attempt to repair it myself.

Got an email from my tech this morning. I described the issue I am having with the amp to him in an earlier email. Here is what he said:

That series of Sansui amps had a problem with the
glue they used to hold down some of the caps during
wave soldering. Over time it became corrosive and
even conductive. There is a pre-driver board (The
vertical one) that needs the glue scraped off and
any corroded parts replaced.

The protection relay is also on this board and it could
also be the culprit - dirty contacts.

I doubt that it would be the outputs, transistors die or
maybe get leaky but rarely heal themselves.

And no, at the moment I cannot get the amp to him, and he really likes to work on Yamaha's. He is a good guy with a great deal of experience.

at lower volumes, the 717 and 919 series when older have a common problem with channel drop out. two main causes are either a dirty volume pot or a cold solder joint on a PCB that acts like an open at low volumes. I would try cleaning the volume pot first.
And as others have suggested, a recap at some point is highly recommended. When these units were made, Sansui used a glue to hold the PCB components in place prior to wave soldering. Over the years, this glue will chemically react with the component leads, and in some cases eat completely through the lead. If you have any cap work done, be sure to clean off all the old glue.
best

I went through and cleaned all the switches. Something I did not do initially. Seems like it's working fine now. Ran it for a few hours last night. And about an hour + on the lowest volume setting.
Man this is an awfully nice sounding unit. Are these modern amps built like this that much better? Especially some of the more expensive, small units. What can you get for $500 that is built, and sounds like this. I have been playing around with audio for few years. You have to spend to much to get something comparable. I will say that most vintage receivers are highly overrated, and not worth the money people are spending on the big ones. The Sansui is a bargain.
Johnss thanks for your response, but did you read the post prior to yours?

Congratulations!You found a treasure.These are great sounding amplifiers.I just picked AU719 in excellent condition and I can't believe how good it is.It has power, clarity,3D sound-stage and very good mid-range.In my opinion it is hard to find something sounding so right even for more than $1000.00 today.