Actually this appears to be a pretty old chassis judging by the faceplate which is three generations back. Once upon a time we did have a big run of cover screws that managed to show rust a few years after going into service in humid/salty climates.
This brand of hardware has been long gone for several years now and I doubt if the issue will repeat on anything we have built in the past 7-8 years or so. Of course the guy could has just ask us for some replacement hardware, free of charge of course.
The unit also is pretty high priced for this series of amplifier built before we went to a multi-stage regulated power supply. That was a major sonic improvement.
The cost to upgrade this unit to new would be $799 including new regulated power supply and audio boards and the no extra cost "+" upgrade. His asking price, $1650, plus the upgrade price, $799 equals $2449 plus shipping. A new Ultra+ 550 is $2399. Thus avoid this unit if your thought is to upgrade it to new performance later. We would suggest paying no more than $1500 if you want to come out ahead on the deal. Do note that major upgrades include minor repairs and a new three year AVA parts and labor warranty, but do not include major repairs to sections of the circuits not included in the upgrade (new output devices in this case, main power supply parts, ect.)
If you do your homework, you can come up with new Ultra+ hybrid amplifier performance for less than new price, but probably not with this unit.
Best regards,
Frank Van Alstine