If it has a slight ammonia smell, then it might be electrolytic fluid (dried up) from one of the main power supply caps. It tends to be quite easy to smell. Much in the direction of a stale urine smell.
However, a quick look at an open chassis of this amp illustrates that it is likely the black glue material they used around the periphery of the plug and metal plate interface. It may have originally been viscous/tar like... and not like a solid epoxy, and might move around from heat exposure and time.
If it’s been moving around, then this amplifier might have had a little too much heat exposure while in storage. Capacitors age from heat, whether the capacitor is in use or not. The scale/chart for the aging of capacitors from heat is not linear, it’s almost exponential. It is a notable part of why thermal management for audio gear is such a big deal.
However, a quick look at an open chassis of this amp illustrates that it is likely the black glue material they used around the periphery of the plug and metal plate interface. It may have originally been viscous/tar like... and not like a solid epoxy, and might move around from heat exposure and time.
If it’s been moving around, then this amplifier might have had a little too much heat exposure while in storage. Capacitors age from heat, whether the capacitor is in use or not. The scale/chart for the aging of capacitors from heat is not linear, it’s almost exponential. It is a notable part of why thermal management for audio gear is such a big deal.