Don't worry too much about it, for all the hallaballoo, it's not going to kill it with a 6A fuse.And I promise I'll never put a oversized fuse in again!
Being a stereo amp can be helpful when tracking faults if one side is still working ok.
With details from the working side being used as a comparison against the non working side.
What would be handy would be a signal injector to plonk some amount of signal , again one side, then the other to see where your dodgy side stops.
Or conversely, again plonk a signal in the front end and using the other half of a simple signal signal injector ( the amp) see where that starts and stops.
Note:- an old transistor radio is ideal to make such a mother.
Split the signal and the amp at the volume control, one end for signal, t'other for amp.