It is repairable.
I have an 8000A, and have just replaced three of the phono socket pairs, because their plastic had become brittle with age (and heat?), and had taken some impacts during a move or two over the years (I've had the amp since the early '80s). Result was that they were crumbling away and not connecting properly.
Anyway, you can get replacements from CPC. Their part number for double-pair sets (as used for CD+Tuner, Tape1 in+out, Tape2 in+out) is CN04160. These are gold plated (unlike the originals), and are drop-in replacements, however you will need to cut off the plastic locator tongues on the bottom, to get them to sit down on the PCB.
You do not have to completely disassemble the amp to get at the PCB to replace these, just sort of (carefully) loosen it a bit so that you can work the phono sockets in and out at an angle. You will need the tools and skills/know-how, though, to remove the old phonos without ripping up the PCB tracks, and to solder in the new ones. It's not really a big deal, if you're familiar with this sort of thing, but there is potential for messing it up if you're not.
HTH,
Dave.