The most common problem with these amps is the capacitors. This is a very well known problem. Over time they leak and need to be replaced. If the leaking is bad, that may cause problems with some of the boards. Sourcing high quality replacements has been an issue over the years.
There is also a rubber damping strip that can melt over time and leak onto components, although the caps are the most common problem.
Call the authorized repair places above and get estimates. Sometimes it is a flat rate, sometimes it is a flat labor rate plus parts. Shipping is also not trivial. My information is several years old, so give them a call and get the current situation.
If you search on Levinson equipment for sale there is a guy who buys non-working equipment.